Daniel Araújo Gay

Verified email at uca.es

Science Faculty
Cadiz University



                                    

http://researchid.co/daniel.araujouca.es

Prof. Daniel ARAUJO is Dr. in Science and physicist of the EPFL Switzerland, (PhD in 1992). Nowadays, he is Full Professor at University of Cadiz (Spain, since 2010) in the Department of Material Science and Engineering and at the Lyon Institute of Technology (INSA-Lyon, France, since 2004, presently in détachement). His activity is actually focused on two different topics: (i) aerospace materials in collaboration with Airbus and FIDAMC (Foundation for Research, Development and Application of Composite Materials), (ii) Homoepitaxial diamond for power devices. In the latter, he is responsible of H2020 and national projects. He has been supervisor of 11 doctoral theses and is author of more than 140 JCR publications and 16 invited/plenary conferences.

EDUCATION

1-. Universidad de Cádiz: Cadiz, Andalucía, ES
1993-01-01 hasta 1994-12-01 | (Ciencias de los Materiales Ingeniería Metalúrgica y Química Inorgánica)

2-. IBM Zurich Research Laboratory: Zurich, Zürich, CH
1992-08-01 hasta 1993-02-01Education

3-. École Polytechnique Fédérale de Lausanne: Lausanne, VD, CH
1988-10-01 hasta 1992-09-30 | (Instituto de micro-optoelectrónica (IMO)

4-. Ecoles du canton de Vaud: Lausanne, Cantón de Vaud, CH
1982-01-01 hasta 1988-01-01 |

5-. École Polytechnique Fédérale de Lausanne: Lausanne, VD, CH
1982-10-01 hasta 1987-06-01 |

129

Scopus Publications

1467

Scholar Citations

21

Scholar h-index

48

Scholar i10-index

Scopus Publications

  • Impact of methane concentration on surface morphology and boron incorporation of heavily boron-doped single crystal diamond layers
    Rozita Rouzbahani, Shannon S. Nicley, Danny E.P. Vanpoucke, Fernando Lloret, Paulius Pobedinskas, Daniel Araujo, and Ken Haenen

    Carbon, ISSN: 00086223, Volume: 172, Pages: 463-473, Published: February 2021 Elsevier BV

  • Diamond/γ-alumina band offset determination by XPS
    J. Cañas, G. Alba, D. Leinen, F. Lloret, M. Gutierrez, D. Eon, J. Pernot, E. Gheeraert, and D. Araujo

    Applied Surface Science, ISSN: 01694332, Volume: 535, Published: 1 January 2021 Elsevier BV
    Abstract γ-Alumina is a promising candidate for fabricating the gate of the diamond metal oxide semiconductor field effect transistor based on oxygen termination due to its high bandgap of 6.7 eV and high static dielectric constant of 9. Besides these properties, having a sufficient barrier for holes is mandatory to avoid carriers leakage through the gate. However, the band offset of the diamond/alumina heterojunction can be affected by the alumina crystallinity and interface bonds, which depend on multiple factors such as deposition and annealing temperature or diamond surface treatment prior to deposition. In this work, the heterojunction of atomic layer deposited alumina and (1 0 0) p-diamond is studied using X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy studies reveal that the deposited alumina layer is 35 nm thick and present the gamma phase. The valence band offset between diamond and γ-alumina is evaluated on a single sample with a new methodology based on an ion etching XPS depth profile. The obtained value for the valence band offset of diamond and γ-alumina is 3.4 eV.

  • Lattice performance during initial steps of the Smart-Cut™ process in semiconducting diamond: A STEM study
    J.C. Piñero, J. de Vecchy, D. Fernández, G. Alba, J. Widiez, L. Di Cioccio, F. Lloret, D. Araujo, and J. Pernot

    Applied Surface Science, ISSN: 01694332, Volume: 528, Published: 30 October 2020 Elsevier BV

  • Interfacial integrity enhancement of atomic layer deposited alumina on boron doped diamond by surface plasma functionalization
    A. Jaggernauth, R.M. Silva, M.A. Neto, F.J. Oliveira, I.K. Bdikin, M.P. Alegre, M. Gutiérrez, D. Araújo, J.C. Mendes, and R.F. Silva

    Surface and Coatings Technology, ISSN: 02578972, Volume: 397, Published: 15 September 2020 Elsevier BV
    Abstract High dielectric constant (high-κ) thin films are ubiquitous in research as they impart enhanced properties to microelectronic applications. Novel combinations for coupling high-κ and ultra-wide band gap semiconductors are being investigated for niche applications, dependent on the environmental conditions for device operation. Typically, high-κ films such as alumina are deposited by atomic layer deposition (ALD), a technique heavily dependent on surface chemistry. This work investigates the effect of plasma surface functionalization of boron doped diamond (BDD) semiconducting films on interface quality with top-layers of ALD alumina (AlO) films, by analyzing its susceptibility to deformation; being particularly vital for electronics subjected to physically demanding environments. Alumina thin films were deposited unto as-grown (AlO-H-BDD) and O2 plasma treated (AlO-O-BDD) polycrystalline BDD. XPS analysis performed on plasma exposed BDD films, prior to AlO deposition, demonstrated a 3% increase in O surface ligands compared to the as-grown surface. Nanoindentation analysis demonstrated plastic deformation within the alumina layer for AlO-O-BDD, for the tested loads, whereas AlO-H-BDD experienced film delamination and deformation beyond the alumina-BDD interface. TEM analysis revealed that delamination was most likely due to low cohesive strength of alumina near the interface, explained by fewer –OH and –CO (ether) BDD surface ligands on H-BDD.

  • Analysis by HR-STEM of the Strain Generation in InP after SiN x Deposition and ICP Etching
    M. Gutiérrez, D. F. Reyes, D. Araujo, J. P. Landesman, and E. Pargon

    Journal of Electronic Materials, ISSN: 03615235, eISSN: 1543186X, Pages: 5226-5231, Published: 1 September 2020 Springer Science and Business Media LLC
    Microelectronic processing to fabricate electronic devices on Si has been extensively studied and well characterized for several decades. This type of processing has been extrapolated for the fabrication of devices on other semiconducting materials such as group III–V materials, SiGe and SiC. However, the structural damage and its functional implication are still not fully understood for sensitive materials like InP. The present work investigates the lattice strain induced by the inductively coupled plasma dry etching process on InP stripes fabricated after masking the stripes with plasma-enhanced chemical vapor deposition-grown SiNx. High-resolution scanning transmission electron microscopy observations allowed us to deduce the strain at different locations in the fabricated stripes. Local strains in the range of 10−3 are observed, which should strongly modify the material carrier behaviour.

  • Surface states of (100) o-terminated diamond: Towards other 1 × 1:O reconstruction models
    Gonzalo Alba, M. Pilar Villar, Rodrigo Alcántara, Javier Navas, and Daniel Araujo

    Nanomaterials, eISSN: 20794991, Pages: 1-15, Published: June 2020 MDPI AG
    Diamond surface properties show a strong dependence on its chemical termination. Hydrogen-terminated and oxygen-terminated diamonds are the most studied terminations with many applications in the electronic and bioelectronic device field. One of the main techniques for the characterization of diamond surface terminations is X-ray photoelectron spectroscopy (XPS). In this sense, the use of angleresolved XPS (ARXPS) experiments allows obtaining depth-dependent information used here to evidence (100)Oterminated diamond surface atomic configuration when fabricated by acid treatment. The results were used to compare the chemistry changes occurring during the oxidation process using a sublayer XPS intensity model. The formation of nondiamond carbon phases at the subsurface and higher oxygen contents were shown to result from the oxygenation treatment. A new (100) 1 × 1:O surface reconstruction model is proposed to explain the XPS quantification results of Oterminated diamond.

  • Study of Early Stages in the Growth of Boron-Doped Diamond on Carbon Fibers
    Josué Millán-Barba, Marina Gutiérrez, Fernando Lloret, Roberto Guzmán de Villoria, Rodrigo Alcántara, Ken Haenen, and Daniel Araujo

    Physica Status Solidi (A) Applications and Materials Science, ISSN: 18626300, eISSN: 18626319, Published: 2020 Wiley

  • How to Grow Fully (100) Oriented SiC/Si/SiC/Si Multi-Stack
    Taguhi Yeghoyan, Kassem Alassaad, Véronique Soulière, Gabriel Ferro, Marina Gutierrez, and Daniel Araujo

    Physica Status Solidi (A) Applications and Materials Science, ISSN: 18626300, eISSN: 18626319, Volume: 216, Published: 22 May 2019 Wiley

  • High resolution boron content profilometry at δ-doping epitaxial diamond interfaces by CTEM
    J.C. Piñero, F. Lloret, M.P. Alegre, M.P. Villar, A. Fiori, E. Bustarret, and D. Araújo

    Applied Surface Science, ISSN: 01694332, Volume: 461, Pages: 221-226, Published: 15 December 2018 Elsevier BV
    Abstract Ultimate spatial resolution in boron δ-doped homoepitaxial diamond interfaces has been achieved by diffraction contrast technique in Transmission Electron Microscopy. The combination of two reflections with the Howie-Whelan equations allows profiling the boron content of δ-doped diamond homoepitaxial layers by fitting experimentally measured CTEM intensities with the theoretical ones. To validate the method, the obtained doping profiles are compared with that of secondary ion mass spectrometry, obtaining a boron concentration of 1.6·1021 at/cm−3, which is in good agreement with that of SIMS. This approach is capable to perform dopant concentration quantification in a non-destructive way, and provides the possibility of nanometric resolution dopant concentration mapping by TEM.

  • Determination of alumina bandgap and dielectric functions of diamond MOS by STEM-VEELS
    J. Cañas, J.C. Piñero, F. Lloret, M. Gutierrez, T. Pham, J. Pernot, and D. Araujo

    Applied Surface Science, ISSN: 01694332, Volume: 461, Pages: 93-97, Published: 15 December 2018 Elsevier BV
    Abstract Alumina is a promising candidate for fabricating the gate of diamond metal oxide semiconductor field effect transistor (MOSFET) due to its outstanding nominal properties: A high gap of 8.8 eV and a high static dielectric constant of 9. However, such properties are strongly dependent on the synthesis. As gate oxides are usually very thin layers (5–50 nm), investigating its properties is not straightforward. Electron energy loss spectroscopy in scanning transmission electron microscopy (STEM-EELS) methodology is reported in the nm-scale range. Monochromatic 60 keV electron beam is used to obtain the low energy loss spectrum in order to allow an accurate zero loss peak deconvolution and to avoid Cherenkov effect. The low energy loss spectrum is used to extract the bandgap along diamond-alumina interface and to perform Kramers-Kronig analysis to obtain the complex dielectric function of the Al2O3. High resolution electron microscopy (HREM) and STEM-EELS investigations show that the oxide phase of our sample is γ alumina. Its measured bandgap is 6.8 eV and the dielectric functions yield a value of 3 for the high frequency dielectric constant.

  • Three-Dimensional Diamond MPCVD Growth over MESA Structures: A Geometric Model for Growth Sector Configuration
    Fernando Lloret, Daniel Araújo, David Eon, and Etienne Bustarret

    Crystal Growth and Design, ISSN: 15287483, eISSN: 15287505, Pages: 7628-7632, Published: 5 December 2018 American Chemical Society (ACS)
    The overgrowth of {100}-oriented patterned diamond substrates by microwave plasma enhanced chemical vapor deposition was studied by transmission electron microscopy through a stratigraphic approach. A sector-like growth behavior is evidenced, resulting from a competition between slowly growing facets at protruding (top) corners and edges against quickly growing facets at recessing (bottom) corners. Depending on the pattern orientation and height, under some particular experimental conditions, it is possible to predict the sequence of growth sectors, and thus to choose the crystallographic orientation of the overgrown surface, by stopping the growth at the right stage. A simple two-dimensional model is provided, allowing the fabrication of structures adapted to the requirements of specific electronic devices.

  • Calibration of a cohesive model for fracture in low cross-linked epoxy resins
    Dery Torres, Shu Guo, Maria-Pilar Villar, Daniel Araujo, and Rafael Estevez

    Polymers, eISSN: 20734360, Published: 28 November 2018 MDPI AG
    Polymer-based composites are becoming widely used for structural applications, in particular in the aeronautic industry. The present investigation focuses on the mechanical integrity of an epoxy resin of which possible damage results in limitation or early stages of dramatic failure. Therefore, a coupled experimental and numerical investigation of failure in an epoxy resin thermoset is carried out that opens the route to an overall micromechanical analysis of thermoset-based composites. In the present case, failure is preceded by noticeable plasticity in the form of shear bands similar to observations in ductile glassy polymers. Thus, an elastic-visco-plastic constitutive law initially devoted to glassy polymer is adopted that captures the rate- dependent yield stress followed by softening and progressive hardening at continued deformation. A general rate-dependent cohesive model is used to describe the failure process. The parameters involved in the description are carefully identified and used in a finite element calculation to predict the material’s toughness for different configurations. Furthermore, the present work allows investigation of nucleation and crack growth in such resins. In particular, a minimum toughness can be derived from the model which is difficult to evaluate experimentally and allows accounting for the notch effect on the onset of failure. This is thought to help in designing polymer-based composites.

  • Crystalline defects induced during MPCVD lateral homoepitaxial diamond growth
    Fernando Lloret, David Eon, Etienne Bustarret, and Daniel Araujo

    Nanomaterials, eISSN: 20794991, Published: 10 October 2018 MDPI AG
    The development of new power devices taking full advantage of the potential of diamond has prompted the design of innovative 3D structures. This implies the overgrowth towards various crystallographic orientations. To understand the consequences of such growth geometries on the defects generation, a Transmission Electron Microscopy (TEM) study of overgrown, mesa-patterned, homoepitaxial, microwave-plasma-enhanced, chemical vapor deposition (MPCVD) diamond is presented. Samples have been grown under quite different conditions of doping and methane concentration in order to identify and distinguish the factors involved in the defects generation. TEM is used to reveal threading dislocations and planar defects. Sources of dislocation generation have been evidenced: (i) doping level versus growth plane, and (ii) methane concentration. The first source of dislocations was shown to generate <110> Burgers vector dislocations above a critical boron concentration, while the second induces <112> type Burgers vector above a critical methane/hydrogen molar ratio. The latter is attributed to partial dislocations whose origin is related to the dissociation of perfect ones by a Shockley process. This dissociation generated stacking faults that likely resulted in penetration twins, which were also observed on these samples. Lateral growth performed at low methane and boron content did not exhibit any dislocation.

  • GaSb and GaSb/AlSb Superlattice Buffer Layers for High-Quality Photodiodes Grown on Commercial GaAs and Si Substrates
    M. Gutiérrez, F. Lloret, P. Jurczak, J. Wu, H. Y. Liu, and D. Araújo

    Journal of Electronic Materials, ISSN: 03615235, Pages: 5083-5086, Published: 1 September 2018 Springer Science and Business Media LLC
    The objective of this work is the integration of InGaAs/GaSb/GaAs heterostructures, with high indium content, on GaAs and Si commercial wafers. The design of an interfacial misfit dislocation array, either on GaAs or Si substrates, allowed growth of strain-free devices. The growth of purposely designed superlattices with their active region free of extended defects on both GaAs and Si substrates is demonstrated. Transmission electron microscopy technique is used for the structural characterization and plastic relaxation study. In the first case, on GaAs substrates, the presence of dopants was demonstrated to reduce several times the threading dislocation density through a strain-hardening mechanism avoiding dislocation interactions, while in the second case, on Si substrates, similar reduction of dislocation interactions is obtained using an AlSb/GaSb superlattice. The latter is shown to redistribute spatially the interfacial misfit dislocation array to reduce dislocation interactions.

  • Control of the alumina microstructure to reduce gate leaks in diamond MOSFETs
    Marina Gutiérrez, Fernando Lloret, Toan Pham, Jesús Cañas, Daniel Reyes, David Eon, Julien Pernot, and Daniel Araújo

    Nanomaterials, eISSN: 20794991, Published: August 2018 MDPI AG
    In contrast to Si technology, amorphous alumina cannot act as a barrier for a carrier at diamond MOSFET gates due to their comparable bandgap. Indeed, gate leaks are generally observed in diamond/alumina gates. A control of the alumina crystallinity and its lattice matching to diamond is here demonstrated to avoid such leaks. Transmission electron microscopy analysis shows that high temperature atomic layer deposition, followed by annealing, generates monocrystalline reconstruction of the gate layer with an optimum lattice orientation with respect to the underneath diamond lattice. Despite the generation of γ-alumina, such lattice control is shown to prohibit the carrier transfer at interfaces and across the oxide.

  • Boron-doping proximity effects on dislocation generation during non-planar MPCVD homoepitaxial diamond growth
    Fernando Lloret, David Eon, Etienne Bustarret, Alexandre Fiori, and Daniel Araujo

    Nanomaterials, eISSN: 20794991, Published: July 2018 MDPI AG
    Epitaxial lateral growth will be required if complex diamond-based device architecture, such as, for example, Metal-oxide-semiconductor Field-effect transistors (MOSFETs) or epitaxial lateral overgrowth (ELO) substrates, need to be developed for high-power applications. To this end, undoped and doped non-planar homoepitaxial diamond were overgrown on (001)-oriented diamond-patterned substrates. Defects induced by both the heavy boron doping and three-dimensional (3D) growth were studied by transmission electron microscopy (TEM). At high methane and boron concentrations, threading dislocations with Burgers vectors b = 1/6 ⟨211⟩, b = 1/2 ⟨110⟩, or both were observed. Their generation mechanisms were established, revealing boron proximity effects as precursors of dislocations generated in boron-doped samples and providing clues as to the different Burgers vectors. The concentration ranges of boron and methane resulting in good crystalline quality depended on the plane of growth. The microwave plasma-enhanced chemical vapour deposition (MPCVD) growth conditions and the maximum boron concentration versus plane orientation yielding a dislocation-free diamond epitaxial layer were determined.

  • Impact of Nonhomoepitaxial Defects in Depleted Diamond MOS Capacitors
    T. T. Pham, J. C. Pinero, A. Marechal, M. Gutierrez, F. Lloret, D. Eon, E. Gheeraert, N. Rouger, D. Araujo, and J. Pernot

    IEEE Transactions on Electron Devices, ISSN: 00189383, Pages: 1830-1837, Published: May 2018 Institute of Electrical and Electronics Engineers (IEEE)

  • High quality Al2O3/(100) oxygen-terminated diamond interface for MOSFETs fabrication
    T. T. Pham, M. Gutiérrez, C. Masante, N. Rouger, D. Eon, E. Gheeraert, D. Araùjo, and J. Pernot

    Applied Physics Letters, ISSN: 00036951, Volume: 112, Published: 5 March 2018 AIP Publishing
    In this letter, we report on the improvement of gate controlled Al2O3/(100) boron doped (B-doped) oxygen-terminated diamond (O-diamond) Metal Oxide Semiconductor Capacitors using 40 nm thick Al2O3 deposited by Atomic Layer Deposition at 380 °C and then annealed at 500 °C in vacuum conditions. The high quality of Al2O3 and an Al2O3/diamond interface is verified thanks to electrical measurements and Transmission Electron Microscopy (TEM) measurements. A density of interface states lower than 1012 eV−1 cm−2 is measured from the flat-band regime to the depletion regime. The shift of the flat-band voltage and the leakage current through the oxide are significantly reduced in good agreement with the mono-crystalline character of the Al2O3 layer revealed by TEM.In this letter, we report on the improvement of gate controlled Al2O3/(100) boron doped (B-doped) oxygen-terminated diamond (O-diamond) Metal Oxide Semiconductor Capacitors using 40 nm thick Al2O3 deposited by Atomic Layer Deposition at 380 °C and then annealed at 500 °C in vacuum conditions. The high quality of Al2O3 and an Al2O3/diamond interface is verified thanks to electrical measurements and Transmission Electron Microscopy (TEM) measurements. A density of interface states lower than 1012 eV−1 cm−2 is measured from the flat-band regime to the depletion regime. The shift of the flat-band voltage and the leakage current through the oxide are significantly reduced in good agreement with the mono-crystalline character of the Al2O3 layer revealed by TEM.

  • Oxygen termination of homoepitaxial diamond surface by ozone and chemical methods: An experimental and theoretical perspective
    Javier Navas, Daniel Araujo, José Carlos Piñero, Antonio Sánchez-Coronilla, Eduardo Blanco, Pilar Villar, Rodrigo Alcántara, Josep Montserrat, Matthieu Florentin, David Eon, and Julien Pernot

    Applied Surface Science, ISSN: 01694332, Volume: 433, Pages: 408-418, Published: 1 March 2018 Elsevier BV
    Abstract Phenomena related with the diamond surface of both power electronic and biosensor devices govern their global behaviour. In particular H- or O-terminations lead to wide variations in their characteristics. To study the origins of such aspects in greater depth, different methods to achieve oxygen terminated diamond were investigated following a multi-technique approach. DFT calculations were then performed to understand the different configurations between the C and O atoms. Three methods for O-terminating the diamond surface were performed: two physical methods with ozone at different pressures, and an acid chemical treatment. X-ray photoelectron spectroscopy, spectroscopic ellipsometry, HRTEM, and EELS were used to characterize the oxygenated surface. Periodic-DFT calculations were undertaken to understand the effect of the different ways in which the oxygen atoms are bonded to carbon atoms on the diamond surface. XPS results showed the presence of hydroxyl or ether groups, composed of simple C O bonds, and the acid treatment resulted in the highest amount of O on the diamond surface. In turn, ellipsometry showed that the different treatments led to the surface having different optical properties, such as a greater refraction index and extinction coefficient in the case of the sample subjected to acid treatment. TEM analysis showed that applying temperature treatment improved the distribution of the oxygen atoms at the interface and that this generates a thinner amount of oxygen at each position and higher interfacial coverage. Finally, DFT calculations showed both an increase in the number of preferential electron transport pathways when π bonds and ether groups appear in the system, and also the presence of states in the middle of the band gap when there are π bonds, C C or C O.

  • Microwave Permittivity of Trace sp2 Carbon Impurities in Sub-Micron Diamond Powders
    Jerome Alexander Cuenca, Evan Lloyd Hunter Thomas, Soumen Mandal, David John Morgan, Fernando Lloret, Daniel Araujo, Oliver Aneurin Williams, and Adrian Porch

    ACS Omega, eISSN: 24701343, Pages: 2183-2192, Published: 28 February 2018 American Chemical Society (ACS)
    Microwave dielectric loss tangent measurements are demonstrated as a method for quantifying trace sp2-hybridized carbon impurities in sub-micron diamond powders. Appropriate test samples are prepared by vacuum annealing at temperatures from 600 to 1200 °C to vary the sp2/sp3 carbon ratio through partial surface graphitization. Microwave permittivity measurements are compared with those obtained using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The average particle size remains constant (verified by scanning electron microscopy) to decouple any geometric dielectric effects from the microwave measurements. After annealing, a small increase in sp2 carbon was identified from the XPS C 1s and Auger spectra, the EELS σ* peak in the C 1s spectra, and the D and G bands in Raman spectroscopy, although a quantifiable diamond to G-band peak ratio was unobtainable. Surface hydrogenation was also evidenced in the Raman and XPS O 1s data. Microwave cavity perturbation measurements show that the dielectric loss tangent increases with increasing sp2 bonding, with the most pertinent finding being that these values correlate with other measurements and that trace concentrations of sp2 carbon as small as 5% can be detected.

  • Silicon (001) heteroepitaxy on 3C-SiC(001)/Si(001) seed
    Taguhi Yeghoyan, Kassem Alassaad, Sean R.C. McMitchell, Marina Gutierrez, Véronique Soulière, Daniel Araújo, and Gabriel Ferro

    Materials Science Forum, ISSN: 02555476, eISSN: 16629752, Volume: 924 MSF, Pages: 128-131, Published: 2018 Trans Tech Publications, Ltd.
    We report for the first time the successful heteroepitaxial growth of Si(100) oriented layer on top of a 3C-SiC(001) seed. By using a post-growth modification of the 3C-SiC surface (pulse insertion of precursors during cooling), it led to a change in Si nucleation, favoring squared (100) islands instead of elongated (110) ones. Without this surface modification step, the Si layers grown on 3C-SiC were always polycrystalline with a mixture of (110) and (100) orientations. Using such Si(100) layer grown on top of 3C-SiC(100), a (100) oriented 3C-SiC single crystalline layer was successfully grown on top, fabricating thus for the first time a fully (100) oriented multilayer heterostructure made of Si(substrate)/SiC/Si/SiC.

  • MPCVD Diamond Lateral Growth Through Microterraces to Reduce Threading Dislocations Density
    Fernando Lloret, Marina Gutierrez, Daniel Araujo, David Eon, and Etienne Bustarret

    Physica Status Solidi (A) Applications and Materials Science, ISSN: 18626300, eISSN: 18626319, Volume: 214, Published: November 2017 Wiley
    Diamond lateral growth is a useful technique to assess 3D architectures of devices. The requirement of the overgrowth on etched substrates has been observed to have additional benefit in the crystallinity of the diamond. The surface roughness is enhanced and threading dislocation density is reduced as a consequence of the lateral growth on patterned substrates. Under these premises, this contribution presents a study of defects and terrace coalescences for the lateral growth on a trenched surface substrates with different trench widths. The latter was achieved on 100-oriented HPHT diamond substrates grown by MPCVD and using very thin-doped layers to mark the growth plane every 100 nm. The results showed high density of threading dislocations that were gathered to the centre of the coalescence. These threading dislocations, as well as planar defects, were investigated using transmission electron microscopy. The mechanism of those defects generation and the better conditions to achieve defect-free areas are discussed.

  • Impact of Thermal Treatments in Crystalline Reconstruction and Electrical Properties of Diamond Ohmic Contacts Created by Boron Ion Implantation
    José C. Piñero, María P. Villar, Daniel Araujo, Josep Montserrat, Bernat Antúnez, and Philippe Godignon

    Physica Status Solidi (A) Applications and Materials Science, ISSN: 18626300, eISSN: 18626319, Volume: 214, Published: November 2017 Wiley
    To obtain p-type doping of diamond through B ion implantation, thermal treatments are necessary to reconstruct the diamond lattice and to locate B atoms in substitutional lattice positions. The present contribution evaluates by STEM-EELS and CL spectroscopy the amorphisation of diamond lattice under the B+ bombardment and its subsequent reconstruction after the thermal treatment. In addition, TEM observations allowed localizing the boron spatial distribution. Carbon-related peaks of EELS spectroscopy shows a nearly complete recovery of the diamond lattice after thermal treatment. Indeed, at 1600 °C, sp2/sp3 ratio in implanted regions changes from 0.56 to 0.18 (0.15 value was measured before implantation). On the other hand, CL spectroscopy reveals how A-Band and free exciton emission peaks, which are quenched by B+ implantation, recover after annealing. Boron ion implantation was used to create ohmic contacts in two different diamond samples, treated with different annealing velocities. Crystalline reconstruction, evidenced by TEM data explains the related electric behaviour. Nanoscale evidences of amorphisation, lattice reconstruction and dopant activation are presented and discussed in this work.

  • Solid solution strengthening in GaSb/GaAs: A mode to reduce the TD density through Be-doping
    M. Gutiérrez, D. Araujo, P. Jurczak, J. Wu, and H. Liu

    Applied Physics Letters, ISSN: 00036951, Volume: 110, Published: 27 February 2017 AIP Publishing
    The need for a low bandgap semiconductor on a GaAs substrate for thermophotovoltaic applications has motivated research on GaSb alloys, in particular, the control of plastic relaxation of its active layer. Although interfacial misfit arrays offer a possibility of growing strain-free GaSb-based devices on GaAs substrates, a high density of threading dislocations is normally observed. Here, we present the effects of the combined influence of Be dopants and low growth temperature on the threading dislocation density observed by Transmission Electron Microscopy. The Be-related hardening mechanism, occurring at island coalescence, is shown to prevent dislocations to glide and hence reduce the threading dislocation density in these structures. The threading density in the doped GaSb layers reaches the values of seven times less than those observed in undoped samples, which confirms the proposed Be-related hardening mechanism.

  • Twins and strain relaxation in zinc-blende GaAs nanowires grown on silicon
    J.C. Piñero, D. Araújo, C.E. Pastore, M. Gutierrez, C. Frigeri, A. Benali, J.F. Lelièvre, and M. Gendry

    Applied Surface Science, ISSN: 01694332, Volume: 395, Pages: 195-199, Published: 15 February 2017 Elsevier BV
    Abstract To integrate materials with large lattice mismatch as GaAs on silicon (Si) substrate, one possible approach, to improve the GaAs crystalline quality, is to use nanowires (NWs) technology. In the present contribution, NWs are grown on 〈111〉 oriented Si substrates by molecular beam epitaxy (MBE) using vapor-liquid-solid (VLS) method. Transmission electron microscopy (TEM) analyses show that NWs are mainly grown alternating wurtzite and zinc blend (ZB) phases, and only few are purely ZB. On the latter, High Resolution Electron Microscopy (HREM) evidences the presence of twins near the surface of the NW showing limited concordance with the calculations of Yuan (2013) [1], where {111} twin planes in a 〈111〉-oriented GaAs NW attain attractive interactions mediated by surface strain. In addition, such twins allow slight strain relaxation and are probably induced by the local huge elastic strain observed by HREM in the lattice between the twin and the surface. The latter is attributed to some slight bending of the NW as shown by the inversion of the strain from one side to the other side of the NW.

  • Atomic composition of WC/ and Zr/O-terminated diamond Schottky interfaces close to ideality
    J.C. Piñero, D. Araújo, A. Fiori, A. Traoré, M.P. Villar, D. Eon, P. Muret, J. Pernot, and T. Teraji

    Applied Surface Science, ISSN: 01694332, Volume: 395, Pages: 200-207, Published: 15 February 2017 Elsevier BV
    Abstract Electrical and nano-structural properties of Zr and WC-based Schottky power diodes are compared and used for investigating oxide-related effects at the diamond/metal interface. Differences in Schottky barrier heights and ideality factors of both structures are shown to be related with the modification of the oxygen-terminated diamond/metal interface configuration. Oxide formation, oxide thickness variations and interfacial oxygen redistribution, associated with thermal treatment are demonstrated. Ideality factors close to ideality (n WC  = 1.02 and n Zr  = 1.16) are obtained after thermal treatment and are shown to be related with the relative oxygen content at the surface (OCR WC  = 3.03 and OCR Zr  = 1.5). Indeed, thermal treatment at higher temperatures is shown to promote an escape of oxygen for the case of the WC diode, while it generates a sharper accumulation of oxygen at the metal/diamond interface for the case of Zr diode. Therefore, the metal-oxygen affinity is shown to be a key parameter to improve diamond-based Schottky diodes.

  • Influence of methane concentration on MPCVD overgrowth of 100-oriented etched diamond substrates
    Fernando Lloret, Daniel Araujo, David Eon, María del Pilar Villar, Juan-María Gonzalez-Leal, and Etienne Bustarret

    Physica Status Solidi (A) Applications and Materials Science, ISSN: 18626300, eISSN: 18626319, Volume: 213, Pages: 2570-2574, Published: 1 October 2016 Wiley
    Selective diamond growth on etched diamond substrates allows the development of 3D-type device geometries, which can make possible higher capacity, higher surface for contacts and benefits from better properties versus growth orientation. Such structures need the control of lateral growth or lateral etching that guarantee the best epitaxial growth, with a well-faceted surface, with a minimum density of emerging defects in order to limit the current leakage and to improve the breakdown voltage. Previous works used 111-oriented selective growth on etched diamond for lateral p–n junctions or bipolar junction transistors. The behavior of homoepitaxial overgrowth on etched diamond substrates depends directly on growth parameters such as temperature, gas concentration or microwave power that can favor the growth in one specific direction. The present contribution considers the effect of methane concentration during the overgrowth of the mesa pattern. The presence of highly doped intermediate layers allowed following the growth plane orientation in a stratigraphic approach. Faceting and growth velocities were analyzed using scanning and transmission electron microscopes (SEM and TEM).

  • Stratigraphy of a diamond epitaxial three-dimensional overgrowth using doping superlattices
    F. Lloret, A. Fiori, D. Araujo, D. Eon, M. P. Villar, and E. Bustarret

    Applied Physics Letters, ISSN: 00036951, Volume: 108, Published: 2 May 2016 AIP Publishing
    The selective doped overgrowth of 3D mesa patterns and trenches has become an essential fabrication step of advanced monolithic diamond-based power devices. The methodology here proposed combines the overgrowth of plasma-etched cylindrical mesa structures with the sequential growth of dopingsuperlattices. The latter involve thin heavily borondoped epilayers separating thicker undoped epilayers in a periodic fashion. Besides the classical shape analysis under the scanning electron microscope relying on the appearance of facets corresponding to the main crystallographic directions and their evolution toward slow growing facets, the dopingsuperlattices were used as markers in oriented cross-sectional lamellas prepared by focused ion beam and observed by transmission electron microscopy. This stratigraphic approach is shown here to be applicable to overgrown structures where faceting was not detectable. Intermediate growth directions were detected at different times of the growth process and the periodicity of the superlattice allowed to calculate the growth rates and parameters, providing an original insight into the planarization mechanism. Different configurations of the growth front were obtained for different sample orientations, illustrating the anisotropy of the 3D growth.Dislocations were also observed along the lateral growth fronts with two types of Burger vector:b011¯=12[011¯] and b112=16[112]. Moreover, the clustering of these extended defects in specific regions of the overgrowth prompted a proposal of two different dislocation generation mechanisms.

  • Potential barrier heights at metal on oxygen-terminated diamond interfaces
    P. Muret, A. Traoré, A. Maréchal, D. Eon, J. Pernot, J. C. Pinẽro, M. P. Villar, and D. Araujo

    Journal of Applied Physics, ISSN: 00218979, eISSN: 10897550, Volume: 118, Published: 28 November 2015 AIP Publishing
    Electrical properties of metal-semiconductor (M/SC) and metal/oxide/SC structures built with Zr or ZrO2 deposited on oxygen-terminated surfaces of (001)-oriented diamond films, comprised of a stack of lightly p-doped diamond on a heavily doped layer itself homoepitaxially grown on an Ib substrate, are investigated experimentally and compared to different models. In Schottky barrier diodes, the interfacial oxide layer evidenced by high resolution transmission electron microscopy and electron energy losses spectroscopy before and after annealing, and barrier height inhomogeneities accounts for the measured electrical characteristics until flat bands are reached, in accordance with a model which generalizes that by Tung [Phys. Rev. B 45, 13509 (1992)] and permits to extract physically meaningful parameters of the three kinds of interface: (a) unannealed ones, (b) annealed at 350 °C, (c) annealed at 450 °C with the characteristic barrier heights of 2.2–2.5 V in case (a) while as low as 0.96 V in case (c). Pos...

  • Si NWs conversion to Si-SiC core-shell NWs by MBE
    Fernando Lloret, D. Araujo, M.P. Villar, L. Liu, and Konstantinos Zekentes

    Materials Science Forum, ISSN: 02555476, eISSN: 16629752, Volume: 821-823, Pages: 965-969, Published: 2015 Trans Tech Publications, Ltd.
    Si nanowires (NWs) samples have been converted to silicon carbide (SiC) NWs at different conditions of substrate temperature in an ultra-high vacuum using a molecular beam epitaxy (MBE) set-up. Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED) have been in-situ carried out to control the growth process. Scanning electron microscopy (SEM) and conventional transmission electron microscopy (CTEM) have been used to characterize the resulting nanostructures. In addition, the samples have been prepared by focused ion beam (FIB) in order to have electron-transparently lamellas for TEM with the interface nanowire-substrate. SiC/Si shell/core NWs free of planar defects have been obtained for conversion tmpratures lower than 800oC.

  • TEM study of defects versus growth orientations in heavily boron-doped diamond
    F. Lloret, D. Araujo, M. P. Alegre, J. M. Gonzalez-Leal, M. P. Villar, D. Eon, and E. Bustarret

    Physica Status Solidi (A) Applications and Materials Science, ISSN: 18626300, eISSN: 18626319, Volume: 212, Pages: 2468-2473, Published: 2015 Wiley
    Heavy boron-doping layer in diamond can be responsible for the generation of extended defects during the growth processes (Blank et al., Diam. Relat. Mater. 17, 1840 (2008) [1]). As claimed recently (Alegre et al., Appl. Phys. Lett. 105, 173103 (2014) [2]), boron pair interactions rather than strain-related misfit seems to be responsible for such dislocation generation. In the present work, electron microscopy observations are used to study the defects induced by heavy boron doping in different growth plane orientations. Facets of pyramidal Hillocks (PHs) and pits provide access to non-conventional growth orientations where boron atoms incorporation is different during growth. TEM analysis on FIB prepared lamellas confirm that also for those growth orientations, the generation of dislocations occurs within the heavily boron-doped diamond layers. Stacking faults (SFs) have been also observed by high resolution transmission electron microscopy (HREM). From the invisibility criteria, using weak beam (WB) observation, 1/2[11¯0] and 1/6[112¯], Burgers vectors have been identified. Their generation behavior confirms the mechanism reported by Alegre et al. where local in-plane strain effects induced at the growing surface of the diamond lattice by the neighboring of several boron atoms cause the generation of such extended defects.

  • Critical boron-doping levels for generation of dislocations in synthetic diamond
    M. P. Alegre, D. Araújo, A. Fiori, J. C. Pinero, F. Lloret, M. P. Villar, P. Achatz, G. Chicot, E. Bustarret, and F. Jomard

    Applied Physics Letters, ISSN: 00036951, Volume: 105, Published: 27 October 2014 AIP Publishing
    Defects induced by boron doping in diamond layers were studied by transmission electron microscopy. The existence of a critical boron doping level above which defects are generated is reported. This level is found to be dependent on the CH4/H2 molar ratios and on growth directions. The critical boron concentration lied in the 6.5–17.0 × 1020at/cm3 range in the ⟨111⟩ direction and at 3.2 × 1021 at/cm3 for the ⟨001⟩ one. Strain related effects induced by the doping are shown not to be responsible. From the location of dislocations and their Burger vectors, a model is proposed, together with their generation mechanism.

  • Heteroepitaxial CVD growth of 3C-SiC on diamond substrate
    Véronique Soulière, Arthur Vo-Ha, Davy Carole, Alexandre Tallaire, Ovidiu Brinza, Jose Carlos Pinero, Daniel Araújo, and Gabriel Ferro

    Materials Science Forum, ISSN: 02555476, eISSN: 16629752, Volume: 778-780, Pages: 226-229, Published: 2014 Trans Tech Publications, Ltd.
    This work presents the successful CVD heteroepitaxial growth of 3C-SiC on diamond (100) substrates. When performing a direct SiC growth at 1500°C on such substrate, it leads to polycrystalline deposit. The use of a substrate pretreatment involving silicon deposition allows forming a more continuous and smoother layer. Electron BackScatter Diffraction and Transmission Electron Microscopy all revealed that the 3C-SiC layer grown on the (100) diamond substrate is monocrystalline and well oriented.

  • Metal-oxide-diamond interface investigation by TEM: Toward MOS and Schottky power device behavior
    J. C. Piñero, D. Araujo, A. Traoré, G. Chicot, A. Maréchal, P. Muret, M. P. Alegre, M. P. Villar, and J. Pernot

    Physica Status Solidi (A) Applications and Materials Science, ISSN: 18626300, eISSN: 18626319, Volume: 211, Pages: 2367-2371, Published: October 2014 Wiley
    Metal and oxide distribution in diamond metal–oxide–semiconductor (MOS) structures are characterized using several transmission electron microscopy (TEM) modes at nanometric scale. To understand their electrical behavior, oxygen distribution using electron energy loss spectroscopy (EELS) through the layer structure, high-resolution electron microscopy (HREM), and annular dark field (ADF) observations are reported. Oxide thickness variations, as well as oxygen content variations have been identified and characterized at an atomic resolution. The latter allows to understand the related electrical behavior as, for example, leakages or shortcuts.

  • 3C-SiC seeded growth on diamond substrate by VLS transport
    Arthur Vo-Ha, Mickaël Rebaud, Davy Carole, Mihai Lazar, Alexandre Tallaire, Véronique Soulière, Jose Carlos Pinero, Daniel Araújo, and Gabriel Ferro

    Materials Science Forum, ISSN: 02555476, eISSN: 16629752, Volume: 778-780, Pages: 234-237, Published: 2014 Trans Tech Publications, Ltd.
    This work deals with the localized epitaxial growth of SiC on (100) diamond substrate using the Vapour-Liquid-Solid (VLS) transport. An epitaxial relationship of grown SiC with the seed was succesfully achieved when inserting a silicidation step before the VLS growth. This silicidation consists in the formation of a SiC intermediate layer on the diamond substrate by solid-state reaction with a silicon layer deposited at 1000 or 1350 °C. On the 1350°C formed SiC buffer layer, p-doped 3C-SiC(100) islands elongated in the <110> directions were obtained after VLS growth. For the 1000°C buffer layer, the SiC deposit after VLS growth is much denser but mostly polycrystalline. Interfacial reactivity and diffusion are considered to explain the obtained results.

  • Diamond as substrate for 3C-SiC growth: A TEM study
    F. Lloret, J. Piñero, D. Araujo, M. P. Villar, E. Gheeraert, A. Vo-Ha, V. Soulière, M. Rebaud, D. Carole, and G. Ferro

    Physica Status Solidi (A) Applications and Materials Science, ISSN: 18626300, eISSN: 18626319, Volume: 211, Pages: 2302-2306, Published: October 2014 Wiley
    Vapor–liquid–solid (V–L–S) growth of SiC on (100) diamond substrate is reported. The crystalline quality is evaluated by transmission electron microscopy (TEM). Diffraction contrast (CTEM) observations allowed confirming the growth of fully lattice relaxed SiC 3C-type crystalline structure. Defects as dislocations at the diamond/SiC interface and stacking faults, in the thick SiC layer are revealed by high resolution TEM and CTEM. From the invisibility criteria, using dark field observations, 〈110〉 type Burger vector are identified.

  • Electronic and physico-chemical properties of nanometric boron delta-doped diamond structures
    G. Chicot, A. Fiori, P. N. Volpe, T. N. Tran Thi, J. C. Gerbedoen, J. Bousquet, M. P. Alegre, J. C. Piñero, D. Araújo, F. Jomard, A. Soltani, J. C. De Jaeger, J. Morse, J. Härtwig, N. Tranchant, C. Mer-Calfati, J. C. Arnault, J. Delahaye, T. Grenet, D. Eon, F. Omnès, J. Pernot, and E. Bustarret

    Journal of Applied Physics, ISSN: 00218979, eISSN: 10897550, Volume: 116, Published: August 28, 2014 AIP Publishing
    Heavily boron doped diamond epilayers with thicknesses ranging from 40 to less than 2 nm and buried between nominally undoped thicker layers have been grown in two different reactors. Two types of [100]-oriented single crystal diamond substrates were used after being characterized by X-ray white beam topography. The chemical composition and thickness of these so-called delta-doped structures have been studied by secondary ion mass spectrometry, transmission electron microscopy, and spectroscopic ellipsometry. Temperature-dependent Hall effect and four probe resistivity measurements have been performed on mesa-patterned Hall bars. The temperature dependence of the hole sheet carrier density and mobility has been investigated over a broad temperature range (6 K < T < 450 K). Depending on the sample, metallic or non-metallic behavior was observed. A hopping conduction mechanism with an anomalous hopping exponent was detected in the non-metallic samples. All metallic delta-doped layers exhibited the same mobi...

  • Boron concentration profiling by high angle annular dark field-scanning transmission electron microscopy in homoepitaxial δ-doped diamond layers
    D. Araújo, M. P. Alegre, J. C. Piñero, A. Fiori, E. Bustarret, and F. Jomard

    Applied Physics Letters, ISSN: 00036951, Volume: 103, Published: 22 July 2013 AIP Publishing
    To develop further diamond related devices, the concentration and spatial location of dopants should be controlled down to the nanometer scale. Scanning transmission electron microscopy using the high angle annular dark field mode is shown to be sensitive to boron doping in diamond epilayers. An analytical procedure is described, whereby local boron concentrations above 1020 cm−3 were quantitatively derived down to nanometer resolution from the signal dependence on thickness and boron content. Experimental boron local doping profiles measured on diamond p−/p++/p− multilayers are compared to macroscopic profiles obtained by secondary ion mass spectrometry, avoiding reported artefacts.

  • Diamond underlayer microstructure effect on the orientation of AlN piezoelectric layers for high frequency SAW resonators by TEM
    F. Lloret, D. Araújo, M.P. Villar, J.G. Rodríguez-Madrid, G.F. Iriarte, O.A. Williams, and F. Calle

    Microelectronic Engineering, ISSN: 01679317, Volume: 112, Pages: 193-197, Published: 2013 Elsevier BV
    Display Omitted HighlightsAlN grain has lattice orientation of their c-axis perpendicular to the interface.After 0.5micron, the c-axis is roughly well oriented for piezoelectric applications.The grain size increase with the height in the layer.Two subfamilies of grain orientation are observed: (01-10) and (2-1-10). Due to its mechanical properties, diamond is very attractive as an active material for the fabrication of SAW resonators for high frequency applications. In this work, the synthesis of piezoelectric AlN films by reactive sputtering at room temperature has been optimized on thick diamond layers grown on Si and alumina substrates in order to process high frequency devices. The effect of diamond underlayer microstructure is evaluated by TEM. Two sets of samples are studied, AlN/NCD/Alumina and AlN/MCD/Si. The orientation of the AlN grains is shown to improve with the film thickness and the diamond grain size. For NCD underlayer, the AlN deposited on top is more oriented. Moreover, above 1µm from the AlN/diamond interface, a high degree of the c-axis orientation (perpendicular to the AlN/diamond interface) is demonstrated even though two different grain lattice orientations are shown to coexist: one with the ( 2 1 ? 1 ? 0 ) planes remaining parallel to the TEM-preparation lamella and the other with ( 0 1 1 ? 0 ) planes. The AlN/diamond interface is smooth down to the nm-scale.

  • Quantification of In x Ga 1-x P composition modulation by nanometric scale HAADF simulations
    C.E. Pastore, M. Gutiérrez, D. Araújo, and E. Rodríguez-Messmer

    Applied Surface Science, ISSN: 01694332, Volume: 269, Pages: 138-142, Published: 2013 Elsevier BV
    Abstract Multijunction solar cell efficiency is highly sensitive to structural and chemical variations. These variations can be quantified at nm scale in InGaP/InGaAs/Ge multijunctions using transmission electron microscopy modes, e.g. diffraction contrast (DC-CTEM) and high angle annular dark field (STEM-HAADF). These studies determined the structure and the composition modulation of InGaP layers with sensitivity below 1% of In composition. To quantify the In-related variation, STEM-HAADF profiles are compared to numerically simulated ones. The fit with the experimental contrast shows local variations of 4.25%In for distances below 30 nm.

  • Multi-technique analysis of high quality HPHT diamond crystal
    C. Fernández-Lorenzo, D. Araújo, M. González-Mañas, J. Martín, J. Navas, R. Alcántara, M.P. Villar, and D. Bagriantsev

    Journal of Crystal Growth, ISSN: 00220248, Volume: 353, Pages: 115-119, Published: 15 August 2012 Elsevier BV
    Abstract Fabrication of high quality diamond either for gemmological or for technological applications, is still a challenge. The control of impurity incorporation for doping or to modify the crystal colour should be still improved. The present contribution reports availability of nearly defect free HPHT (high pressure high temperature) diamond in terms of dislocations and point defects. Cathodoluminescence (CL) transitions related to point defects or dislocations (A-band) are not observed and only some individual dislocations are revealed by X-ray topography (topo-X). CL spectra are dominated by the excitonic-related transistions and the boron incorporation, estimated from the phonon-replica relative intensities, is around 1016 cm−3 that corroborate the values estimated by FTIR. Such amount of B gives a pale blue colour to the diamond sintetized monocrystal. The latter crystals are grown at the Instituto de Monocristales S.L. for jewellery applications, but their use for semiconducting applications is also envisaged after the highlights of the present study.

  • Optimization of AlN thin layers on diamond substrates for high frequency SAW resonators
    J.G. Rodríguez-Madrid, G.F. Iriarte, D. Araujo, M.P. Villar, O.A. Williams, W. Müller-Sebert, and F. Calle

    Materials Letters, ISSN: 0167577X, Pages: 339-342, Published: 1 January 2012 Elsevier BV
    AlN/diamond heterostructures are very promising for high frequency surface acoustic wave (SAW) resonators. In their design, the thickness of the piezoelectric film is one of the key parameters. On the other hand, the film material quality and, hence, the device performance, also depend on that thickness. In this work, polished microcrystalline diamond substrates have been used to deposit AlN films by reactive sputtering, from 150 nm up to 3 μm thick. A high degree of the c-axis orientation has been obtained in all cases. SAW one port resonators at high frequency have been fabricated on these films with a proper combination of the film thickness and transducer size.

  • Fabrication of high frequency SAW resonators using AlN/Diamond/Si technology
    G.F. Iriarte, J.G. Rodriguez, R. Ro, R. Lee, O. A. Williams, D. Araujo, M.P. Villar, and F. Calle

    IEEE International Ultrasonics Symposium, IUS, ISSN: 19485719, eISSN: 19485727, Pages: 573-576, Published: 2011 IEEE
    The synthesis of AlN on diamond is a great challenge, not only because of the between an AlN/diamond interface, but also because of the high surface roughness of the diamond layers [8, 9]. In the case of microcrystalline diamond, the last problem was solved by polishing. However, polishing nanocrystalline diamond is not straightforward. For the diamond synthesis by CVD, silicon was used as a substrate. The diamond/Si interface presents a smoother diamond than the diamond/air interface. This paper reports on the fabrication of high frequency SAW resonators using AlN/Diamond/Si technology.

  • Cross sectional evaluation of boron doping and defect distribution in homoepitaxial diamond layers
    Daniel Araújo, M. A. Paz Alegre, Antonio J. García, M. Pilar Villar, Etienne Bustarret, Philipp Achatz, Pierre N. Volpe, and Franck Omnès

    Physica Status Solidi (C) Current Topics in Solid State Physics, ISSN: 18626351, eISSN: 16101642, Pages: 1366-1370, Published: April 2011 Wiley
    In some diamond-based semiconducting devices, large variations of doping level are required over short distances. Tools to determine doping level and defects distribution should therefore be developed. The present contribution shows the capabilities of electron microscopy in this field. Focused ion beam (FIB-dual beam) cross section preparations allowed evaluating doping level in highly boron doped sample with doping transition down to some nm by diffraction contrast mode of transmission electron microscopy (CTEM) and by high angle annular dark field mode of scanning transmission electron microscopy (HAADF-STEM). The sensibility of the latter is around 1019cm-3 and, thus, cathodoluminescence (CL) is required for lower doping levels. Cross sectional analysis on FIB prepared lamella allowed to separate the epilayer behaviour from that of the substrate. Mid-gap centers involving boron, hydrogen and, for some peaks, also nitrogen are revealed. sp2 bonds are also present in the grown epilayer. These transitions make difficult the observation of excitonic recombinations in the cross section configuration.

  • Influence of the substrate type on CVD grown homoepitaxial diamond layer quality by cross sectional TEM and CL analysis
    D. Araújo, M.P. Alegre, A.J. García, J. Navas, M.P. Villar, E. Bustarret, P.N. Volpe, and F. Omnès

    Diamond and Related Materials, ISSN: 09259635, Pages: 428-432, Published: March 2011 Elsevier BV
    Abstract To assess diamond-based semiconducting devices, a reduction of point defect levels and an accurate control of doping are required as well as the control of layer thickness. Among the analyses required to improve such parameters, cross sectional studies should take importance in the near future. The present contribution shows how FIB (focused ion beam) preparations followed by electron microscopy related techniques as TEM or CL allowed to perform analysis versus depth in the layer, doping and point defect levels. Three samples grown along the same week in the same machine with identical growth conditions but on different substrates (CVD-IIIa (110) oriented, CVD-optical grade (100) oriented and a HPHT-Ib (100) oriented) are studied. Even though A-band is observed by CL, no dislocation is observed by CTEM. Point defect type and level are shown to substantially change with respect to the substrate type as well as the boron doping levels that vary within an order of magnitude. H3 present in the epilayer grown on HPHT type of substrate is replaced by T1 and NE3 point defects for epilayers grown on the CVD type one. An increase of excitonic transitions through LO phonons is also shown to take place near the surface while only TO ones are detected deeper in the epilayer. Such results highlight the importance of choosing the correct substrate.

  • Sputter optimization of AlN on diamond substrates for high frequency SAW resonators
    J. G. Rodriguez, G. F. Iriarte, F. Calle, D. Araujo, M. P. Villar, and O. A. Williams

    Proceedings of the 8th Spanish Conference on Electron Devices, CDE'2011, Published: 2011 IEEE
    The AlN/diamond structure is an attractive combination for SAW devices and its application at high frequencies. In this work, the synthesis of AlN thin films by reactive sputtering has been optimized on diamond substrates in order to process high frequency devices. Polished microcrystalline and as-grown nanocrystalline diamond substrates have been used to deposit AlN of different thickness under equal sputtering conditions. For the smoother substrates, the FWHM of the rocking curve of the (002) AlN peak varies from 3.8° to 2.7° with increasing power. SAW one port resonators have been fabricated on these films, whose electrical characterization (in terms of S11 parameters) is reported.

  • TEM study of superconducting polycrystalline diamond
    M. P. Alegre, M. P. Villar, D. Araújo, E. Bustarret, T. Capron, O. A. Williams, Gabriel Ferro, and Paul Siffert

    AIP Conference Proceedings, ISSN: 0094243X, eISSN: 15517616, Volume: 1292, Pages: 133-136, Published: 2010 AIP
    Heavily Boron‐doped MPCVD‐grown (Microwave Plasma Chemical Vapour Deposition) polycrystalline diamond layers were observed to have a superconducting character depending exclusively on the growth time, i.e. grown under identical experimental conditions. To elucidate such behavior, morphology aspects are investigated using Transmission Electron Microscopy (TEM). Diffraction contrasts and High Angle Annular Dark Field (HAADF) observations show that grains are thicker and boron enrichment occur at grain boundary in the superconducting samples. Interfacial effects are the main difference between the two samples, in the non‐superconducting ones descohesion effect is observed. In both samples boron concentration is nearly constant except in isolated grains and twins, where their crystal orientation probably influences boron incorporation during growth. In summary, as grain configuration changes along the growth, a threshold thickness should be over passed to allow an optimum transport between the diamond grains.

  • Spatially correlated microstructure and superconductivity in polycrystalline boron-doped diamond
    F. Dahlem, P. Achatz, O. A. Williams, D. Araujo, E. Bustarret, and H. Courtois

    Physical Review B - Condensed Matter and Materials Physics, ISSN: 10980121, eISSN: 1550235X, Published: 30 July 2010 American Physical Society (APS)
    Scanning tunneling spectroscopies are performed below 100 mK on polycrystalline boron-doped diamond films characterized by transmission electron microscopy and transport measurements. We demonstrate a strong correlation between the local superconductivity strength and the granular structure of the films. The study of the spectral shape, amplitude, and temperature dependence of the superconductivity gap enables us to differentiate intrinsically superconducting grains that follow the BCS model, from grains showing a different behavior involving the superconducting proximity effect.

  • Composition modulation analysis of In x Ga 1-x P layers grown on (0 0 1) germanium substrates
    C.E. Pastore, D. Araújo, M. Gutiérrez, J. Miguel-Sánchez, and E. Rodríguez-Messmer

    Applied Surface Science, ISSN: 01694332, Volume: 256, Pages: 5681-5683, Published: 1 July 2010 Elsevier BV
    Abstract The development of new photovoltaic approach to improve costs and efficiencies is focused on the new materials and new technologies. InGaP is, in this sense, a key material for solar conversion. In particular, in the solar concentration approach, this material is part of multiple junction solar cells. Its low lattice mismatch with germanium and its adequate bandgap make it very promising. This paper shows how compositional modulation can affect the InGaP emitter and the AlGaAs tunnel junctions. The influence of the growth conditions, on the compositional modulation and misfit and threading dislocations, in In 0.49 Ga 0.51 P layers is demonstrated by TEM on purposely grown single InGaP layers. High resolution electron microscopy (HREM) intensity profiles showed no elastic lattice related modulation.

  • Local boron doping quantification in homoepitaxial diamond structures
    D. Araújo, P. Achatz, R. El Bouayadi, A.J. García, M.P. Alegre, M.P. Villar, F. Jomard, and E. Bustarret

    Diamond and Related Materials, ISSN: 09259635, Issue: 7-9, Pages: 972-975, Published: July 2010 Elsevier BV
    article i nfo Available online 1 March 2010 The capability of transmission electron microscopy (TEM) using the high angle annular dark field mode (HAADF, also labelled Z-contrast) to quantify boron concentration, in the high doping range between 10 19 cm −3 and 10 21 cm −3 ,isdemonstrated.ThankstothelargerelativevariationofatomicnumberZbetweencarbonandboron, doping concentration maps and profiles are obtained with a nanometer-scale resolution. A novel numerical simulation procedure allows the boron concentration quantification and demonstrates the high sensitivity and spatial resolution of the technique.

  • Hydrogen passivation of boron acceptors in as-grown boron-doped CVD diamond epilayers
    C. Fernández-Lorenzo, D. Araújo, J. Martín, R. Alcántara, J. Navas, M.P. Villar, M.P. Alegre, P.N. Volpe, F. Omnès, and E. Bustarret

    Diamond and Related Materials, ISSN: 09259635, Issue: 7-9, Pages: 904-907, Published: July 2010 Elsevier BV
    Abstract A homoepitaxial boron-doped diamond single layer is investigated by means of Fourier transformed infrared spectroscopy (FTIR) and cathodoluminescence (CL). Both techniques are shown to be complementary. µ-FTIR mapping allows to determine the location of active boron while CL allows discernability between passivation and compensation. Hydrogen incorporation during chemical vapour deposition (CVD) growth is revealed to passivate boron acceptors. The obtained results highlight that plasma etching can induce a dissociation of B–H centres.

  • Mechanism of phase separation generation in ge-based solar cell tunnel junctions
    M. Gutiérrez, C. E. Pastore, D. Araújo, J. Miguel-Sánchez, and E. Rodríguez-Messmer

    Journal of Nanoscience and Nanotechnology, ISSN: 15334880, Pages: 1166-1170, Published: February 2010 American Scientific Publishers
    Enhanced performance, reduced cost and compact dimensions are a prerequisite for novel products in the solar industry. III-V based multi-junction heterostructures are promising devices to give an answer to make a substancial step in the photovoltaic technology. However, such heterostructures need tunnel junctions to connect the different active layers and so ternary alloys are needed to tune the energy gap. In the present contribution, artefacts generated by ternary alloying are investigated by transmission electron microscopy (TEM). Composition modulation in In0.015Ga0.985As/In0.3Ga0.7P/Al0.3Ga0.7As/In0.3Ga0.6Al0.1P/In0.3Al0.7P/In0.015Ga0.985As heterostructures grown on Ge subtrates is observed. This should affect the spectral sensitivity of the active layer. But, as a probably more important consequence, this observed modulation is shown to also generate modulation in the Al0.3Ga0.7As tunnel junction. This behaviour is anomalous in standard AIGaAs thick epilayers grown on GaAs substrates. In the present case, it could strongly affect the carrier transport imposing an important handicap to their potential application within electro-optical components.

  • InAs/GaAs quantum dots morphology: Nanometric scale HAADF simulations
    D. Araújo, R. El Bouayadi, M. Gutiérrez, C.E. Pastore, and M. Hopkinson

    Materials Science and Engineering B: Solid-State Materials for Advanced Technology, ISSN: 09215107, Volume: 165, Issue: 1-2, Pages: 88-93, Published: 25 November 2009 Elsevier BV
    Abstract A quantitative methodology of In distribution in nominal InAs/GaAs individual quantum dot (QD) is presented. Numerical simulations, using multislice-based approach, allow predicting high angle annular dark field (HAADF or Z-contrast) micrograph contrasts working in scanning transmission electron microscopy (STEM) mode. Even the method is adapted for nanometric scale; it is shown that its high sensitivity can reveal In-segregation in QD. The here observed samples show In diffusion below the wetting layer giving an elliptical-like shape of the observed QD.

  • A microstructural study of superconductive nanocrystalline diamond
    M. P. Villar, Ma. P. Alegre, D. Araujo, E. Bustarret, P. Achatz, L. Saminadayar, C. Bauerle, and O. A. Williams

    Physica Status Solidi (A) Applications and Materials Science, ISSN: 18626300, eISSN: 18626319, Volume: 206, Pages: 1986-1990, Published: September 2009 Wiley
    A transmission electron microscopy (TEM) study of superconducting nanocrystalline diamond (NCD) continuous layers is reported. The high resolution transmission electron microscopy (HREM) and the diffraction contrast modes of observations are used to reveal the nanograins configuration. Three types of them are observed: first, close to the interface with the Si/SiO2 substrate, 10–20 nm-sized diamond seeds resulting from the 5 nm size diamond powder deposition before growth that show some regrowth during CVD process, second a diamond overgrown layer, quasi-epitaxially by coalesced larger NCD grains, and finally, up to the free surface, a thin disordered region composed of nanocrystallites smaller than 6 nm. This last layer was not nominally expected and is attributed to a renucleated-like (RND) carbon layer embedding ultra NCD grains. Diffraction contrast observations confirm this HREM observed behavior.

  • Electro-optical characterisation for the control of silicon nanocrystals embedded in SiNx:H films
    J.-F. Lelièvre, H. Rodriguez, E. Fourmond, S. Quoizola, M. Lipinski, D. Araujo, G. Bremond, and M. Lemiti

    Physica Status Solidi (C) Current Topics in Solid State Physics, ISSN: 18626351, Pages: 1554-1559, Published: 2007 Wiley
    Institute of Metallurgy and Materials Science, Polish Academy of Science, Reymonta 25, 30-059 Krakow, Poland3 GEMPPM, UMR CNRS 5510, INSA de Lyon, 69621 Villeurbanne Cedex, France Received 12 May 2006, revised 21 July 2006, accepted 6 September 2006 Published online 30 March 2007 PACS 61.46.Hk, 73.50.Pz, 78.55.Qr, 78.67.Bf, 81.07.Bc In this work, electro-optical characterization techniques were used to control the size and density of sili-con nanocrystals (nc-Si) in situ grown in non-stoichiometric amorphous hydrogenated silicon nitride (SiN

  • Evidence of intrinsic silicon nanostructure formation in SiN matrix deposited by various low temperature CVD techniques
    J.-F. Lelièvre, H. Rodriguez, E. Fourmond, S. Quoizola, J. De la Torre, A. Sibai, G. Bremond, P.-J. Ribeyron, J.-C. Loretz, D. Araujo, and M. Lemiti

    Physica Status Solidi (C) Current Topics in Solid State Physics, ISSN: 18626351, Pages: 1401-1405, Published: 2007 Wiley
    In this work, we report the intrinsic formation of silicon nanostructures (ns-Si) in non-stoechiometric amorphous hydrogenated silicon nitride (SiNx:H) obtained by different deposition techniques (UltraViolet photo-assisted Chemical Vapour Deposition and Low-Frequency Plasma-Enhanced CVD using two different reactors). No post-deposition treatment was needed. The obtained layers were characterized by photoluminescence (PL) and photocurrent (PC) spectroscopy, revealing emission/absorption mechanisms dominated by confined excitons within ns-Si. Transmission electron microscopy (TEM) confirmed the presence of these ns-Si, in a crystalline form, for SiNx:H layers obtained by both LF-PECVD reactors. Thus, quantum confinement effect could be identified for every deposition techniques involved, revealing the formation of intrinsic ns-Si in the amorphous SiN matrix. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

  • Structural characterization of InN quantum dots grown by Metalorganic Vapour Phase Epitaxy
    J. G. Lozano, D. González, A. M. Sánchez, D. Araújo, S. Ruffenach, O. Briot, and R. García

    Physica Status Solidi (C) Current Topics in Solid State Physics, ISSN: 18626351, Pages: 1687-1690, Published: 2006 Wiley
    The effect of a low temperature GaN capping layer on the structural properties of InN quantum dots is reported. InN quantum dots grown onto sapphire using GaN buffer, with and without low temperature GaN capping layer, have been investigated by atomic force microscopy and transmission electron microscopy. The analysis revealed hexagonal shape quantum dots in both samples. Moreover, the GaN capping layer gives rise to a reduction in the dots aspect ratio. Moire fringe patterns, obtained in planar view geometry, were used to analyse the strain relaxation of the InN quantum dots. The moire pattern measurements demonstrated that the uncapped InN quantum dot is almost fully relaxed. These results are related to the formation of a 60° misfit dislocation network in the InN/GaN interface. However, the capping layer not only generated a change of the aspect ratio, but also a decrease in the heterostructure plastic relaxation. The reason of this effect is discussed.

  • Correlation of optical and photoluminescence properties in amorphous SiNx:H thin films deposited by PECVD or UVCVD
    J.-F. Lelièvre, J. De la Torre, A. Kaminski, G. Bremond, M. Lemiti, Rachid El Bouayadi, Daniel Araujo, Thierry Epicier, R. Monna, M. Pirot, P.-J. Ribeyron, and C. Jaussaud

    Thin Solid Films, ISSN: 00406090, Volume: 511-512, Pages: 103-107, Published: 26 July 2006 Elsevier BV
    Abstract Hydrogenated silicon nitride SiN x :H films are largely used as antireflective coating as well as passivation layer for industrial crystalline and multicrystalline silicon solar cells. This work is focused on the optical and photoluminescence (PL) properties of SiN x :H deposited by either Plasma-Enhanced Chemical Vapour Deposition (PECVD) or UltraViolet photo-assisted CVD (UVCVD). Photoluminescence phenomena were investigated in SiN x :H having different stoechiometries. On the other hand, spectroscopic ellipsometry was carried out in order to obtain the optical properties of the films, from which the optical gap could be determined. The evolution of the photoluminescence with stoechiometry was correlated to the evolution of the optical properties, and especially the absorption within the SiN x :H layer. A good agreement was found considering the confinement of excitons in strongly absorbing silicon nanostructures (ns-Si) formed in the SiN x matrix, with different sizes according to the NH 3  / SiH 4 gas flow ratio and the deposition technique. The main PL peak showed an increase of the emission intensity along with a blueshift as silicon concentration decreases. These observations indicate a radiative recombination mechanism dominated by confined excitons within ns-Si rather than emission related to defects. Furthermore, these ns-Si are supposed to be responsible of the global higher absorption, and hence lower optical gap, of the near-stoechiometric SiN x :H films in comparison with the stoechiometric Si 3 N 4 ones. These assumptions were confirmed thanks to transmission electron microscopy (TEM) images performed on one of the samples, showing crystalline silicon quantum dots (c-Si QDs) embedded in the SiN x matrix.

  • Nucleation of InN quantum dots on GaN by metalorganic vapor phase epitaxy
    J. G. Lozano, A. M. Sánchez, R. García, D. González, D. Araújo, S. Ruffenach, and O. Briot

    Applied Physics Letters, ISSN: 00036951, Pages: 1-3, Published: 2005 AIP Publishing
    InN quantum dots (QDs) on GaN (0001) grown by metalorganic vapor phase epitaxy onto a sapphire substrate were studied by transmission electron microscopy (TEM). We found that the nucleation of InN QDs on GaN is directly related to the presence of threading dislocations (TDs) in the center of the QDs. The TEM analysis revealed that the TDs finish at the InN∕GaN interface and they are pure edge dislocations. Therefore, spiral growth models cannot explain nucleation of these QDs. Although controlling edge TDs constitute a possible approach to determine the QD density, a better approach may be an increase in the material growth rate in order to enter the diffusion-limited growth mode, where growth is not sensitive to surface heterogeneities.

  • Excitonic emission and N- And B-incorporation in homoepitaxial CVD-grown diamond investigated by cathodoluminescence
    D. Araujo, M. Kadri, M. Wade, E. Bustarret, and A. Deneuville

    Physica Status Solidi C: Conferences, ISSN: 16101634, Pages: 1336-1341, Published: 2005 Wiley
    Diamond is a very large bandgap material arising high expectations either for optoelectronic applications or for active semiconducting layers in specific electronic devices to be used under extreme conditions of pressure, temperature, wear or radiation, as well as in chemically aggressive environments. Unintentionally boron-doped diamond layers were grown by microwave plasma-assisted chemical vapour deposition (CVD) on {001}-oriented undoped Ib substrates with the addition of oxygen gas during growth. The relative quantities of nitrogen and boron incorporated in the diamond lattice are evaluated by cathodoluminescence (CL) spectra recorded at 5 K. Two different effects are shown to limit nitrogen incorporation: the substrate crystalline quality and the addition of oxygen into the precursor during the growth. First, the CL spectra are shown to change strongly near the edges of the substrate in the regions corresponding to different bulk crystal growth modes. Some regions show a luminescence governed by UV emission while in other regions, where the H3 defect-related luminescence of the substrate is much stronger, the film UV emission is reduced. Second, the relative importance of the free exciton emission with respect to those from the nitrogen-related H3 centre and from the boron-bound exciton is shown to increase with the addition of oxygen during growth. Such observations are of first importance to improve the spectral emission and absorption threshold of the diamond material in the deep UV range. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

  • Effect of oxygen on the cathodoluminescence signal from excitons, impurities and structural defects in homoepitaxial (100) diamond films
    M. Kadri, D. Araujo, M. Wade, A. Deneuville, and E. Bustarret

    Diamond and Related Materials, ISSN: 09259635, Issue: 3-7, Pages: 566-569, Published: March 2005 Elsevier BV
    Cathodoluminescence at 5 K is used to study the residual radiative defects in homoepitaxial diamond films deposited on the centre of the plasma ball versus the O/CH4 ratio from 0 to 0.375 in the feeding gas, and to understand their effect on the quality (intensity of the free exciton peaks) of the films. The addition of oxygen significantly reduces the slight boron contamination (1.610 16 to 410 14 cm 3 ) of these good quality (BE NP exciton peak) non-intentionally doped films. As the O/C ratio increases, (i) the intensities of the boron-bound excitons, Nc–Vc, H3, Nc–Ic peaks, of the 2.3 eV wide band and the nitrogen contamination decrease (ii) the intensity of the N3 peak and the relative intensity of the A band increase. These opposite variations of the defects concentration as O/C increases result in a maximum of the FE peaks for O/C around 0.25. D 2004 Elsevier B.V. All rights reserved.

  • Defect morphology and strain of CVD grown 3C-SiC layers: Effect of the carbonization process
    D. Méndez, A. Aouni, F. M. Morales, F. J. Pacheco, D. Araújo, E. Bustarret, G. Ferro, and Y. Monteil

    Physica Status Solidi (A) Applications and Materials Science, ISSN: 18626300, eISSN: 18626319, Volume: 202, Pages: 561-565, Published: March 2005 Wiley
    The heterostructure formed by cubic silicon carbide/silicon (3C-SiC/Si) is very promising as substrate for cubic III-N growth and for SiC devices. Optimized Si substrate carbonization process before the epitaxial growth of SiC, leads to a higher quality of the layer. In this paper, transmission electron microscopy is used to analyze the defect morphology and strain of SiC layers grown by chemical vapor deposition on two differently carbonized substrates, with tensile and compressive strain state. Misfit dislocations, stacking faults and antiphase domains are observed in this heteroepitaxial system. Irrespective of the substrate used, the epitaxial relationship between Si and SiC is good. However, the grain misorientation of the mosaic structure and the strain of the overgrowth layer depend drastically on the carbonization conditions of the silicon substrate.

  • Study of isolated cubic GaN quantum dots by low-temperature cathodoluminescence
    J.P. Garayt, J.M. Gérard, F. Enjalbert, L. Ferlazzo, S. Founta, E. Martinez-Guerrero, F. Rol, D. Araujo, R. Cox, B. Daudin, B. Gayral, Le Si Dang, and H. Mariette

    Physica E: Low-Dimensional Systems and Nanostructures, ISSN: 13869477, Issue: 1-4, Pages: 203-206, Published: February 2005 Elsevier BV
    We report single dot spectroscopy of cubic GaN/AlN self-assembled quantum dots. Typical linewidths of the zero-phonon line between 2 and 8 meV are observed and interpreted in terms of charge fluctuations around a given quantum dot. The phonon sideband contribution in this emission, even at low temperature, reveals the importance of the acoustic phonon broadening mechanism which controls the exciton dephasing and may impose the real limits to the optical properties of GaN single QDs emission.

  • Planar defects, voids and their relationship in 3C-SiC layers
    David Méndez, A. Aouni, Daniel Araújo, Gabriel Ferro, Yves Monteil, and Etienne Bustarret

    Materials Science Forum, ISSN: 02555476, eISSN: 16629752, Volume: 483-485, Pages: 189-192, Published: 2005 Trans Tech Publications Ltd.

  • Analysis of SiC islands formation during first steps of Si carbonization process
    David Méndez, A. Aouni, Daniel Araújo, Etienne Bustarret, Gabriel Ferro, and Yves Monteil

    Materials Science Forum, ISSN: 02555476, eISSN: 16629752, Volume: 483-485, Pages: 555-558, Published: 2005 Trans Tech Publications Ltd.

  • Excitons and defects in homoepitaxial diamond films from cathodoluminescence of p-/p+ samples
    M. Wade, M. Kadri, E. Bustarret, A. Deneuville, P. Muret, and D. Araujo

    Physica Status Solidi (A) Applied Research, ISSN: 00318965, Volume: 201, Pages: 2457-2461, Published: September 2004 Wiley
    We study the signals from excitons and defects from the cathodoluminescence spectra (CL) of the p - /pseudo substrate sample. The CL from the p - film are determined from the variation of the CL of the sample as the voltage of the exciting electron beam increases. At the lower voltages, it probes the p - film. The CL is dominated by the free exciton associated with the TO phonon (FE TO , FWHM = 6 meV), but shows also small signals (ratio = 5 x 10 -2 ) mainly from the A band (and other 2.6, 3.6 and 4.05 eV wide bands) and tiny signals from the 5 RL defect. At the higher voltages it probes also the Ib substrate and is dominated by the signals of the H3 defects in the Ib substrate. The p - film appears almost homogeneous, and of good quality from the characteristics of its exciton.

  • Homoepitaxial {111}-oriented diamond pn junctions grown on B-doped Ib synthetic diamond
    A. Tajani, C. Tavares, M. Wade, C. Baron, E. Gheeraert, E. Bustarret, S. Koizumi, and D. Araujo

    Physica Status Solidi (A) Applied Research, ISSN: 00318965, Volume: 201, Pages: 2462-2466, Published: September 2004 Wiley
    Boron- and phosphorus-doped diamond layers were grown successively by microwave plasma-assisted chemical vapour deposition on {111}-oriented boron-doped Ib substrates. The resulting diodes were studied electrically with and without metallization. Although cathodoluminescence results showed that the material quality of the p-type {111} layer could still be improved, Electron Beam Induced Current imaging (EBIC) provided evidence for a space charge region. At room temperature, I(V) characteristics yielded a rectification ratio at +/- 25V varying between 10 4 and 10 9 . In some cases, this figure remained greater than 10 6 up to 200 °C, despite a marked increase of the reverse current with temperature.

  • The role of Ge predeposition temperature in the MBE epitaxy of SiC on silicon
    F. M. Morales, Ch. Zgheib, S. I. Molina, D. Araújo, R. García, C. Fernández, A. Sanz-Hervás, P. Masri, P. Weih, Th. Stauden, V. Cimalla, O. Ambacher, and J. Pezoldt

    Physica Status Solidi C: Conferences, ISSN: 16101634, Pages: 341-346, Published: 2004 Wiley
    An alternative method for stress relaxation in the SiC/Si heteroepitaxial system based on the incorporation of a group-IV element (germanium) into the interface between SiC and Si is presented. We have investigated the effect of the temperature during the predeposition of 1 ML of Ge on a silicon (111) surface, prior to the MBE carbonization. The resulting structures were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR). The crystalline quality of the 3C-SiC layer was improved by the Ge predeposition, as shown by XRD measurements and by the smaller damping constants of the TO and LO phonons in the FTIR analysis. As the temperature of Ge predeposition increases, the SiC layer exhibits lower residual strain and larger grain size. Furthermore, the incorporation of Ge at the interface suppresses the outdiffusion of Si from the substrate to the surface of the growing SiC layer and, therefore, impedes the formation of voids at the SiC/Si interface. TEM and SIMS results revealed a strong segregation of Ge at the interface leading to an increased stress relaxation, in agreement with theoretical predictions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

  • Study of the phosphorus incorporation in n-doped diamond films by cathodoluminescence
    D Araujo, A Tajani, E Gheeraert, and E Bustarret

    Journal of Physics Condensed Matter, ISSN: 09538984, Published: 21 January 2004 IOP Publishing
    The incorporation of phosphorus (P) dopants as donor atoms in chemical vapour deposition (CVD) diamond is studied by cathodoluminescence (CL). P-doped and undoped samples with identical CVD growth conditions are analysed. Variations in the spectral emission of the doped diamond are observed depending on the orientation of growth sectors. Indeed, strain relaxation through crack generation induces the formation of a faceted topography of the substrate surface. Centres associated with P incorporation seem to be responsible for the change in the CL spectral emission in the non-(111) facets. This indicates that n-type diamond can probably be grown on other than (111) orientation. Excitonic emission from liquid He to room temperature is observed for both samples as a result of the high quality n-doped growth.

  • Structural study of micro and nanotubes synthesized by rapid thermal chemical vapor deposition
    Daniel Ara�jo, Rafael Garc�a, Sergio Ignacio Molina, Francisco M. Morales, David M�ndez, and Teresa Ben

    Microchimica Acta, ISSN: 00263672, Volume: 145, Issue: 1-4, Pages: 129-132, Published: 2004 Springer Science and Business Media LLC
    Abstract.The structures of micro and nanotubes obtained by pyrolysis of hydrocarbons, hold onto silicon (Si) substrates, are reported in this work. The tubes fabrication experiments were carried out by Rapid Thermal Chemical Vapor Deposition (RTCVD) using propane (C3H8) as carbon (C) precursor. Selection of parameters such as temperature of deposition, vacuum conditions or surface cleaning leads to the creation of tubular structures. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), selected area electron diffraction (SAED) and energy dispersive X-ray measurements (EDX) are the microbeam techniques that allow to characterize the tubes found in the studied specimens. Different tube configurations such as isolated nanorods, Y-type junctions or fiber-like layers are evidenced. Metallic catalysis seems to be the mechanism involved in the wires formation since Fe particles are present inside the CNT tubes. Other poly-crystalline inclusions are also evidenced by SAED. The composition of the nanotubes changes from tip to tail in an amorphous matrix. The growth mechanisms leading to tube formation are described.

  • Transmission Electron Microscopy study of SiC layers obtained by carbonization of Si wafers
    F. M. Morales, J. Ramírez, C. Fernández, L. Barbadillo, J. Piqueras, D. Araújo, S. I. Molina, and R. García

    Boletin de la Sociedad Espanola de Ceramica y Vidrio, ISSN: 03663175, Pages: 363-366, Published: 2004 Elsevier BV
    The fabrication and characterization of thin SiC layers obtained by Rapid Thermal Chemical Vapour Deposition (RTCVD) are reported. These SiC layers were grown in a simple home-made system for Si wafers carbonization. The growth process was carried out using a mixture of H 2 and C 3 H 8 as the C precursor. (001) Si was carbonized at atmospheric pressure while (111) and (001) Si surfaces were carbonized at vacuum conditions. Scanning electron microscopy (SEM) and transmission electron microscopy in conventional (CTEM), high resolution (HREM), and electron diffraction (TED) modes, as well as reflectivity Fourier transform infra-red spectroscopy (R-FTIR) were the techniques used for the structural and compositional studies of these SiC layers that mainly consisted in highly oriented 3C-SiC.

  • Interfacial strain and defects in Si (001) carbonisation layers for 3C-SiC hetero-epitaxy
    Materials Science Forum, ISSN: 02555476, eISSN: 16629752, Volume: 457-460, Pages: 277-280, Published: 2004

  • Carbon Fiber Reinforced Polymers (CFRP) Nd:YAG laser machining
    Antonio J. García, M. Pilar Villar, Daniel Araújo, J. Fabián García-Motolinia, Elisabet Ribera, Carlos Díez, Clarisa López-Gascón, Carlos Estepa, José I. Peña, and Rafael García

    ICALEO 2004 - 23rd International Congress on Applications of Laser and Electro-Optics, Congress Proceedings, Published: 2004 Laser Institute of America
    Nowadays, carbon fiber reinforced plastics (CFRP) are being widely used in transport industry due to their high mechanical properties and low weight. In this communication, laser machining is studied as an alternative to traditional mechanical machining and drilling for such materials. Nd :YAG laser machining experiments were carried out on CFRP in order to minimize the heat affected zone (HAZ) length and to study the influence of the pressure of the assistant gas N2. Three cutting series were performed, applying different laser operation parameter (power, velocity, gain and frequency). In series 1 and 2 the pressure of the assistant gas is changed (15 bars in series 1, and 5 bars in series 2). The third series of cuts were carried out using cryogenic N2 in order to cool around the cutting zone during laser machining. The following parameters have been studied: velocity, laser beam power, frequency, gain and assistant gas pressure. The influence of these parameters on the HAZ length and depth of the cut in the material has been obtained.Nowadays, carbon fiber reinforced plastics (CFRP) are being widely used in transport industry due to their high mechanical properties and low weight. In this communication, laser machining is studied as an alternative to traditional mechanical machining and drilling for such materials. Nd :YAG laser machining experiments were carried out on CFRP in order to minimize the heat affected zone (HAZ) length and to study the influence of the pressure of the assistant gas N2. Three cutting series were performed, applying different laser operation parameter (power, velocity, gain and frequency). In series 1 and 2 the pressure of the assistant gas is changed (15 bars in series 1, and 5 bars in series 2). The third series of cuts were carried out using cryogenic N2 in order to cool around the cutting zone during laser machining. The following parameters have been studied: velocity, laser beam power, frequency, gain and assistant gas pressure. The influence of these parameters on the HAZ length and depth of the cut i...

  • Influence of the Ge coverage prior to carbonization on the structure of SiC grown on Si(111)
    Francisco M. Morales, Charbel Zgheib, S.I. Molina, Daniel Araújo, R. García, C. Fernández, A. Sanz-Hervás, Pierre M. Masri, Petia Weih, Thomas Stauden, Oliver Ambacher, and Jörg Pezoldt

    Materials Science Forum, ISSN: 02555476, eISSN: 16629752, Volume: 457-460, Pages: 297-300, Published: 2004 Trans Tech Publications, Ltd.

  • Microstructural study of CO 2 laser machined heat affected zone of 2024 aluminum alloy
    D. Araújo, F.J. Carpio, D. Méndez, A.J. Garcı́a, M.P. Villar, R. Garcı́a, D. Jiménez, and L. Rubio

    Applied Surface Science, ISSN: 01694332, Volume: 208-209, Pages: 210-217, Published: 15 March 2003 Elsevier BV
    Abstract Laser machining is an attractive alternative to traditional machining of Al 2024 because critical operation parameters in aeronautic industry like processing time, versatility, contamination and finish can be improved. The main disadvantage of laser machining is the high temperatures reached by the studied material during the laser processing. A heat affected zone (HAZ) extension lower than 5 μm is observed. The microstructural analysis shows that this HAZ suffers a heating between 548 and 596 °C where α-liquid phases are present. The high N 2 gas pressure used for the laser cutting induces three types of roughness on this viscous material during the laser processing. To improve this feature, the use of other laser wavelengths and/or power is proposed. The higher quality of the process can also be reached using other aeronautic materials with lower Cu content as 7475 Al alloy.

  • Fatigue behaviour of laser machined 2024 T3 aeronautic aluminium alloy
    F Carpio

    Applied Surface Science, ISSN: 01694332, Volume: 208-209, Pages: 194-198, Published: 15 March 2003 Elsevier BV
    Abstract High power laser applications as welding, machining and marking are widely used in several industrial sectors to take advantage of their high processing velocity, clean processing conditions, and a high versatility. However, the heat affected zone (HAZ) is expected to change the mechanical behaviour of laser processed structural elements. For aeronautic applications, this feature is of first importance because those elements suffer cyclic stress under service conditions. Indeed, the most severe requirements for further industrial implantation are the fatigue specifications. In this communication, fatigue behaviour of laser machined 2024 aluminium alloy is studied to evaluate a possible certification of laser-based machining in the aeronautic industry. For this reason, 1.6 mm thick samples laser machined were carried out using a CO 2 laser. The experimental fatigue curves are shown to lie very close to aeronautic requirement despite theoretical fatigue behaviour of the material is significantly more resistant. This is attributed to surface roughness induced by a surface melting zone shown that diminish the fatigue resistance. Fatigue behaviour and surface roughness should be improved using higher power and/or high absorption wavelength as that of YAG laser ( λ =1.06 μm).

  • Transmission electron microscopy study of simultaneous high-dose C+ + N+ co-implantation into (1 1 1)Si
    F Morales

    Thin Solid Films, ISSN: 00406090, Volume: 426, Issue: 1-2, Pages: 16-30, Published: 24 February 2003 Elsevier BV
    Abstract A structural electron microscopy study of (1 1 1)Si samples implanted with C + +N + at low energies (30 keV) and high-doses (5×10 17 at. cm −2 for carbon ions and 6.7×10 17 at. cm −2 for nitrogen ions) is reported in this paper. Implantations were carried out both at room and high (600 °C) temperatures. Samples implanted at high temperature and annealed after implantation show a buried layer consisting of a mixture of some amorphous component and single-crystalline crystallites (SiC and probably Si 3 N 4 and C 3 N 4 ) well oriented with respect to the (1 1 1)Si substrate. Both inclusions and amorphous phases are included into a well-aligned Si matrix. The crystalline structure of buried layers resulting after implantation at room and higher temperatures is reviewed. The obtained structural results are confronted to the actual literature. These are encouraging results in order to use the ion implantation to obtain stoichiometric crystalline thin layers.

  • Comparative TEM Investigation of MBE and RTCVD Conversion of Si into SiC
    Francisco M. Morales, S.I. Molina, Daniel Araújo, Volker Cimalla, and Jörg Pezoldt

    Materials Science Forum, ISSN: 02555476, eISSN: 16629752, Volume: 433-436, Pages: 285-288, Published: 2003 Trans Tech Publications, Ltd.

  • SiC voids, mosaic microstructure and dislocations distribution in Si carbonized layers
    F Morales

    Diamond and Related Materials, ISSN: 09259635, Issue: 3-7, Pages: 1227-1230, Published: March/July 2003 Elsevier BV
    Abstract The defect structure of SiC/Si layers obtained by carbonization of Si is reported by means of transmission electron microscopy in high-resolution (HREM) and conventional (CTEM) modes. 3C–SiC was obtained after a rapid thermal annealing treatment and good interfacial quality is reported in terms of small void dimensions and densities. Moreover, high misfit dislocation densities are observed close to the Si/SiC interface and inside the SiC layer without observable generation of threading dislocations. The mosaic grain structure is also evidenced, with low misorientation with respect to the substrate. These results are encouraging for further growth of III–N alloy heterostructures.

  • Transmission electron microscopy study of ultra-thin SiC layers obtained by rapid thermal carbonization of Si wafers
    F. M. Morales, S. I. Molina, D. Araújo, V. Cimalla, J. Pezoldt, L. Barbadillo, M. J. Hernández, and J. Piqueras

    Physica Status Solidi (A) Applied Research, ISSN: 00318965, Volume: 195, Issue: 1 SPEC, Pages: 116-121, Published: January 2003 Wiley
    A structural multitechnique study of β-SiC/Si(111) and β-SiC/Si(100) wafers is reported in this paper. SiC thin layers have been developed in a Rapid Thermal Chemical Vapor Deposition (RTCVD) system by Si carbonization with propane. The study was carried out by High Resolution and Conventional Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED), Spectroscopic Ellipsometry (SE), Fourier Transform Infra-Red Spectroscopy (FTIR) and Single Wave Length Multiple Angle (SWLMA) measurements. The thickness variations of the carbonized layer are determined along radial directions in both wafers by High Resolution Transmission Electron Microscopy (HRTEM). The latter are compared with average thickness determinations obtained by SE. The analyses confirm the existence of β-SiC layers with thicknesses of few nanometers in 3 inch SiC/Si wafers. Plan-view SAED evidences the existence of good structural quality and well aligned (111) and (001) β-SiC layers. Compositional and structural homogeneity indicates a self-limiting conversion mechanism of the Si surface into SiC. These are encouraging results in order to use the Si carbonization to grow stoichiometric crystalline III-N thin layers on Si. In fact, the obtained substrates in this work are actually used for a further GaN overgrowth.

  • Structural Study of GaN Layers Grown on Carbonized Si(111) Substrates
    Materials Science Forum, ISSN: 02555476, eISSN: 16629752, Volume: 433-436, Pages: 1003-1006, Published: 2003

  • Structural characterization of high-dose C++N+ ion-implanted (1 1 1) Si
    L. Barbadillo, M.J. Hernández, M. Cervera, P. Rodrı́guez, J. Piqueras, S.I. Molina, F.M. Morales, and D. Araújo

    Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, ISSN: 0168583X, Volume: 184, Pages: 361-370, Published: November 2001 Elsevier BV
    Abstract (1 1 1) silicon wafers were implanted with high ion doses of C+,N+ and C++N+, from 1×1016 to 6.7×10 17 cm −2 , well over the amorphization dose. For the largest dose, the mean impurity concentration in the implanted region (of about 1000 A) at 30 keV is expected to be similar to the Si atom density. Silicon nitride and silicon carbide formation is detected in the as-implanted samples. After annealing at 1200 °C a trend to segregation of Si3N4 and SiC in separated layers is observed, and a polycrystalline Si overlayer is formed.

  • Radiation response of n-type base InP solar cells
    Robert J. Walters, S. R. Messenger, G. P. Summers, M. J. Romero, M. M. Al-Jassim, D. Araújo, and R. Garcia

    Journal of Applied Physics, ISSN: 00218979, Pages: 3558-3565, Published: 1 October 2001 AIP Publishing
    The effects of particle irradiation on the electrical properties of high efficiency p/n InP solar cells have been studied using a variety of techniques including current–voltage and spectral quantum efficiency measurements (QE), electron beam induced currents (EBIC), and deep level transient spectroscopy. A detailed analysis of the radiation response of the solar cell photovoltaic response is presented, and the primary damage mechanisms are identified. Data measured after irradiation by protons of various energies are correlated in terms of displacement damage dose to produce a characteristic degradation curve for the p/n InP technology. This characteristic curve is compared to that of the n/p InP technology to provide an assessment of the relative radiation hardness of the p/n devices. Radiation-induced decreases in the minority carrier diffusion length in both the p-type emitter and n-type base at low damage levels have been extracted from the QE and EBIC measurements, and damage coefficients have been ...

  • Electron beam induced current and cathodoluminescence study of proton irradiated InAsxP1-x/InP quantum-well solar cells
    Robert J. Walters, G. P. Summers, S. R. Messenger, M. J. Romero, M. M. Al-Jassim, R. Garcia, D. Araujo, A. Freundlich, F. Newman, and M. F. Vilela

    Journal of Applied Physics, ISSN: 00218979, Pages: 2840-2846, Published: 15 September 2001 AIP Publishing
    The effects of proton irradiation on strained InAsxP1−x/InP-based quantum well solar cells (QWSCs) have been investigated by the electron beam induced current (EBIC) and cathodoluminescence (CL) techniques. From analysis of the EBIC data, capture rates within the quantum well region have been estimated, from which the open circuit voltages of the cells were calculated and shown to agree well with the measured values. Diffusion lengths have been estimated from analysis of both the EBIC and CL measurements. The location of the energy levels of proton-induced defects and their effectiveness as nonradiative recombination centers have been determined from Arrhenius plots of the total CL intensity emitted from the quantum wells following irradiation. The results suggest that deeper and narrower quantum wells increase the sensitivity of QWSCs to radiation damage.

  • SiC thin films obtained by Si carbonization
    S.I. Molina, F.M. Morales, and D. Araújo

    Materials Science and Engineering B: Solid-State Materials for Advanced Technology, ISSN: 09215107, Issue: 1-3, Pages: 342-344, Published: 22 March 2001 Elsevier BV
    This work reports the fabrication and characterization of SiC thin films obtained by carbonization of Si substrates with a recently designed and fabricated hot-wall reactor by rapid thermal chemical vapor deposition. The reactor design is less complex than other ones previously reported, but it permits to reach a similar SiC material crystalline quality. The composition and structure of the fabricated thin films have been assessed by scanning electron microscopy and transmission electron microscopy. The structural quality of the obtained films has been optimized as a function of the temperature ramp rate, flowing gases, Si surface pre-treatment and sample holder design. SiC obtained layers on Si exhibit a flat free surface, they mainly consist of highly oriented 3C-SiC and some hexagonal SiC inclusions have been detected.

  • Proton-induced damage in p+-n InP solar cells: The role of electron capture at high fluences
    M.J. Romero, R.J. Walters, D. Araújo, S.R. Messenger, G.P. Summers, R.W. Hoffman, and R. Garcı́a

    Materials Science and Engineering B: Solid-State Materials for Advanced Technology, ISSN: 09215107, Issue: 1-3, Pages: 294-298, Published: 22 March 2001 Elsevier BV
    Abstract Through the technique of electron beam induced current (EBIC), the effects of proton irradiation on InP solar cells of p + – n polarity have been investigated. InP cells of the opposite polarity ( n + – p ) have been shown to collapse under heavy proton irradiation, due to carrier removal that first depletes and eventually type converts the base region. In contrast, we show that for cells of p + – n polarity, electron capture plays the dominant role in the cell radiation response at high damage levels.

  • Control of phase modulation in InGaAs epilayers
    D. González, G. Aragón, D. Araújo, and R. Garcı́a

    Applied Physics Letters, ISSN: 00036951, Pages: 3236-3238, Published: 29 May 2000 AIP Publishing
    A theoretical description of the phase modulation state of epitaxial InGaAs layers has been recently published [D. Gonzalez et al. Appl. Phys. Lett. 74, 2649 (1999)]. To verify experimentally the deduced phase diagram, InGaAs structures with In compositional steps were grown using different growth conditions. Transmission electron microscopy studies have revealed the modulation state in each layer and have allowed us to define the experimental In composition and temperature dependence of the phase transition. The results show that InGaAs layers with and without composition modulation can be obtained by changing the growth temperature. An excellent agreement with the model predictions is observed.

  • Electron beam induced current and cathodoluminescence study of proton irradiated quantum-well solar cells
    R.J. Walters, G.P. Summers, S.R. Messenger, M.J. Romero, D. Araujo, R. Garcia, A. Freundlich, F. Newman, and M.F. Vilela

    Conference Record of the IEEE Photovoltaic Specialists Conference, ISSN: 01608371, Volume: 2000-January, Pages: 1312-1315, Published: 2000 IEEE
    The effects of proton irradiation on InP-based multi-quantum well solar cells (QWSCs) are investigated by the electron beam induced current (EBIC) and cathodoluminescence (CL) techniques. From analysis of the EBIC data, capture rates within the quantum wells are estimated from which the open circuit voltage is calculated and shown to agree well with the measured values. The diffusion length for radiative recombination within the quantum wells is also estimated. From Arrhenius plots of the luminescence excited in quantum wells, the proton irradiation-induced recombination centers are characterized. The results suggest that narrower wells make QWSCs more sensitive to radiation damage.

  • Multiple quantum well GaAs/AlGaAs solar cells: Transport and recombination properties by means of EBIC and cathodoluminescence
    D. Araújo, M.J. Romero, F. Morier-Genoud, and R. Garcı́a

    Materials Science and Engineering B: Solid-State Materials for Advanced Technology, ISSN: 09215107, Pages: 151-156, Published: 1 December 1999 Elsevier BV
    Abstract Multiple quantum well (MQW) p-i-n heterostructures are a new alternative to increase the quantum efficiency of solar cell devices. In such structures, the QW carrier capture, carrier escape and radiative recombinations are the phenomena governing the efficiency of the p-i(MQW)-n solar cell. In this contribution, in spite of the photon-induced current mode of work of such device, an electron beam-induced-current (EBIC) study allowing a very localized carrier excitation is reported. The EBIC measurements are shown to be able to estimate with high accuracy the QWs capture–escape and radiative lifetimes. The latter are determined as a function of the carrier injection level fitting experimental EBIC profiles to simulated ones. Values around 10 −10 and 10 −7 s respectively are obtained.

  • Failure analysis of heavily proton irradiated p+-n InGaP solar cells by EBIC and cathodoluminescence
    M.J. Romero, R.J. Walters, D. Araújo, and R. Garcı́a

    Materials Science and Engineering B: Solid-State Materials for Advanced Technology, ISSN: 09215107, Pages: 189-193, Published: 1 December 1999 Elsevier BV
    Abstract In this paper the effects of heavy proton irradiation on single-junction (SJ) p + -n InGaP solar cells are investigated by means of electron-beam-induced-current (EBIC) and cathodoluminescence (CL). A hole diffusion length reduction from 0.3 to 0.02 μm after 1×10 14 protons/cm 2 irradiation is estimated from EBIC measurements. Such degradation is attributed mainly to IE3 point defects as evidenced by the temperature dependence of the CL intensity. The electronic activity of such defects is shown to be reduced after thermal treatment. Indeed an enhancement of the light emission is observed after electron bombardment only on InGaP while no recovery is observed on the GaAs substrate. Such results illustrate the potential of EBIC/CL in device failure analysis as they are non-destructive techniques.

  • Detailed defect study in proton irradiated InP/Si solar cells
    R. J. Walters, M. J. Romero, D. Araújo, R. Garcı́a, S. R. Messenger, and G. P. Summers

    Journal of Applied Physics, ISSN: 00218979, Pages: 3584-3589, Published: 1 October 1999 AIP Publishing
    A detailed study of the effects of proton irradiation-induced defects in heteroepitaxially grown InP/Si solar cells has been made through a combination of cathodoluminescence (CL), electron beam induced current (EBIC), and electrochemical capacitance versus voltage (ECV) carrier profiling measurements. The CL data indicate the distribution of nonradiative recombination centers both before and after proton irradiation, and temperature dependent and spectroscopic analysis of the CL signal give an estimate of the energies of the dominant defect levels. The EBIC data yield an estimate of the magnitude and spatial variation of the minority carrier diffusion length (L) in the base region. Values of L determined from EBIC measurements made on solar cells irradiated by protons ranging in energy from 0.1 up to 4.5 MeV follow a single curve when plotted versus displacement dose, Dd, allowing a single proton damage coefficient to be determined. The ECV measurements show the evolution of the carrier concentration pro...

  • Spatial distribution of radiation-induced defects in p+-n InGaP solar cells
    M. J. Romero, D. Araújo, R. Garcı́a, R. J. Walters, G. P. Summers, and S. R. Messenger

    Applied Physics Letters, ISSN: 00036951, Pages: 3812-3814, Published: 21 June 1999 AIP Publishing
    The spatial distribution of radiation-induced, radiative recombination centers in single-junction p+-n InGaP solar cells irradiated by 1 MeV electrons or 3 MeV protons has been determined from cathodoluminescence (CL) spectra. The energy levels of the radiation-induced, nonradiative recombination centers were determined from the temperature dependence of the CL intensity.

  • Growth rate and critical temperatures to avoid the modulation of composition of InGaAs epitaxial layers
    D. González, G. Aragón, D. Araújo, M. J. de Castro, and R. García

    Applied Physics Letters, ISSN: 00036951, Pages: 2649-2651, Published: 3 May 1999 AIP Publishing
    Ternary and quaternary semiconductor alloys are usually limited in their band gap engineering by problems related to modulation of composition. In this contribution, we point out the importance of the growth rate in the evolution of a modulation profile in epitaxial films. As a consequence, a diagram of phases for the epitaxial growth is proposed where a window of homogeneous composition is evidenced at low temperatures of growth. The model provides a framework for the epitaxial growth where temperature and growth rate regulation permits the control of the composition modulation in heteroepitaxies.

  • Radiation-induced order-disorder transition in p+-n InGaP solar cells
    M. J. Romero, D. Araújo, R. Garcı́a, R. J. Walters, G. P. Summers, and S. R. Messenger

    Applied Physics Letters, ISSN: 00036951, Pages: 2684-2686, Published: 3 May 1999 AIP Publishing
    The effects of electron and proton irradiation on p+–n InGaP solar cells grown on GaAs substrates are investigated using cathodoluminescence (CL) and transmission electron microscopy (TEM). The CL measurements confirm the higher radiation resistance and defect annealing properties of InGaP compared to those of GaAs. The CL measurements also indicate the occurrence of a radiation-induced sublattice order–disorder transition in InGaP. TEM reveals the presence of ordering domains in the as-grown cells, which are effectively removed by radiation-induced defects. The results should be useful in the fabrication of radiation-resistant single-junction and dual-junction InGaP solar cells for space.

  • Effect of In-content on the misfit dislocation interaction in InGaAs/GaAs layers
    D. Gonzalez, G. Aragón, D, Araújo, and R. García

    Thin Solid Films, ISSN: 00406090, Volume: 343-344, Issue: 1-2, Pages: 302-304, Published: 1999 Elsevier BV
    Abstract A previous published model (D. Gonzalez, D. Araujo, G. Aragon, R. Garcia, Appl. Phys. Lett., 71 (1997) 2477) allows us to predict the plastic relaxation in the saturation regime of epitaxial layers. This model is in agreement with the experimental residual strain for In x Ga 1− x As/ GaAs epilayers below 40% In-content. Above 40% In-content, the predicted values of residual strain become larger than the experimental one. This disagreement takes its origin in the change of growth mode that implies a transition from a 60 ° misfit dislocation (MD) network to a Lomer MD one. An almost complete relaxation can be reached by a Lomer MD network, which is not possible with 60 † MD networks. The difference between both kinds of networks comes from the repulsive interaction of 60 ° MD that inhibits the lattice relaxation.

  • Piezoelectric InGaAs/GaAs (111)B multiple quantum well photodiodes: Optoelectronic properties by electron beam induced current and cathodoluminescence
    M.J. Romero, D. Araújo, J.L. Sánchez-Rojas, E. Calleja, E. Muñoz, and R. Garcı́a

    Microelectronics Journal, ISSN: 00262692, Pages: 413-417, Published: April/May 1999 Elsevier BV
    Abstract As a novel design parameter, the built-in piezoelectric field induced in InGaAs/GaAs (111)B heterostructures has potential applications in novel optoelectronic devices. Negative average field (NAF) and positive average field (PAF) p–i–n photodiodes are here studied by electron beam induced current (EBIC) and cathodoluminescence (CL). As a result of the negative potential envelope, carrier capture and recombination processes in the multiple quantum well (MQW) are shown to govern the carrier dynamic only in NAFs. Indeed, the electron beam induced current carriers become trapped at the potential minima located at the ends of the MQW giving rise to a long-range electric dipole. Using spatially resolved monochromatic cathodoluminescence measurements, a direct evidence of such long-range screening effect in (111) NAF diodes is given.

  • Electron microscopy study of SiC obtained by the carbonization of Si(111)
    F.J. Pacheco, A.M. Sanchez, S.I. Molina, D. Araújo, J. Devrajan, A.J. Steckl, and R. García

    Thin Solid Films, ISSN: 00406090, Volume: 343-344, Issue: 1-2, Pages: 305-308, Published: 1999 Elsevier BV
    A SiC thin film grown by propane carbonization of a Si(111) substrate has been characterized by transmission electron microscopy and scanning electron microscopy techniques. This study reveals the presence of planar defects in the SiC layer and voids in the Si(111) substrate as well as misfit dislocations at the SiC/Si interface. The resulting SiC layer consists of a mosaic structure and is shown to have low stress.

  • Transmission electron microscopy study of InGaAs/InP superlattices grown on V-shaped surface InP substrates
    S.I Molina, D Araujo, T.C Rojas, R Garcia, F Morier-Genoud, U Marti, and F.K Reinhart

    Applied Surface Science, ISSN: 01694332, Volume: 144-145, Pages: 488-491, Published: April 1999 Elsevier BV
    Fabrication of InGaAs/InP quantum well wires obtained by growing InGaAs/InP superlattices on V-grooved surface (001) InP substrates is evidenced. The density of planar defects propagated through the epilayers of these heterostructures depends on the type (A or B) of atoms which constitute the surface of the V-grooved (111) planes. The (111)B V-grooved surfaces are shown to generate more defects propagating through the heterostructure.

  • Critical thickness for the saturation state of strain relaxation in the InGaAs/GaAs systems
    D. González, D. Araújo, G. Aragón, and R. Garcı́a

    Applied Physics Letters, ISSN: 00036951, Pages: 1875-1877, Published: 1998 AIP Publishing
    Using previously published relaxation models [D. J. Dunstan, P. Kidd, L. K. Howard and R. H. Dixon, Appl. Phys. Lett. 59, 3390 (1991) and D. Gonzalez, D. Araujo, G. Aragon, and R. Garcia, Appl. Phys. Lett. 71, 2475 (1997)] that predict the strain relaxation in the InGaAs/GaAs system, before and during the stage of relaxation saturation, the critical thickness where dislocation interactions begin to limit the plastic relaxation is estimated. The approximations used to deduce an analytical expression are shown to be appropriate for describing the regime of relaxation considered. A good agreement with experimental data previously published by other authors permits a physical explanation for the different observed regimes of relaxation to be given.

  • Cathodoluminescence study of heavily proton irradiated heteroepitaxial n+-p InP/Si solar cells
    Solid State Phenomena, ISSN: 10120394, Volume: 63-64, Pages: 497-508, Published: 1998

  • Failure analysis of neutron-irradiated MQW InGaAsP/InP lasers by EBIC
    M. Romero, Daniel Araújo, K. Gill, F. Vasey, and R. García

    Solid State Phenomena, ISSN: 10120394, Volume: 63-64, Pages: 443-456, Published: 1998 Trans Tech Publications, Ltd.

  • Characterisation by TEM and X-ray diffraction of linearly graded composition InGaAs buffer layers on (001) GaAs
    F. J. Pacheco, D. Araújo, S. I. Molina, R. García, A. Sacedón, F. González-Sanz, E. Calleja, P. Kidd, and M. A. Lourenço

    Materials Science and Technology, ISSN: 02670836, Pages: 1273-1278, Published: December 1998 Informa UK Limited
    AbstractThe dislocation distribution in linearly graded composition layers of InGaAs on GaAs is studied by transmission electron microscopy (TEM). Dislocations are shown to penetrate into the substrate and to invade the first part of the graded layer. A simple balance of forces model predicts the presence of dislocations in the substrate. The observed dislocation distribution in the first region of the graded layer is compared to that predicted by several models. The differences between the models' predictions and observations reported here are discussed. The description of the strain relaxation mechanism given by Dunstan's model is shown to give the best fit to the results reported in the present paper.

  • Influence of interface dislocations on surface kinetics during epitaxial growth of InGaAs
    A.L. Álvarez, F. Calle, J.F. Valtuen˜a, J. Faura, M.A. Sánchez, E. Calleja, E. Mun˜oz, J.R. Morante, D. González, D. Araujo, and R. García Roja

    Applied Surface Science, ISSN: 01694332, Volume: 123-124, Pages: 303-307, Published: January 1998 Elsevier BV
    The correlation between surface striations and misfit dislocations at the interface has been studied on In x Ga 1-x As single layers (x < 0.25), as a function of the growth parameters (substrate temperature and deposition rate), by means of atomic force and transmission electron microscopies. It is concluded that both features may be initially linked by mechanical causes (elastic displacement fields), but eventually evolve in a different way due to the surface kinetic effects. The range of growth conditions for an optimum surface quality is determined. A simplified treatment of the diffusion equation, in which the effect of the surface on the dislocation stress field is included, has allowed an estimation of the effective mean free path between collisions for the group III adatoms in the range of a few A.

  • A work-hardening based model of the strain relief in multilayer graded-buffer structures
    D. González, D. Araújo, G. Aragón, and R. Garcı́a

    Applied Physics Letters, ISSN: 00036951, Pages: 3099-3101, Published: 24 November 1997 AIP Publishing
    This paper describes the modeling of the dislocation distribution and of the strain relief in linearly and step-graded structures, based on work-hardening considerations. The model considers the energy variation in an InGaAs/GaAs system upon introducing a new dislocation into the interfacial fixed array of misfit dislocations. An analytical expression for the strain relaxation in graded-buffer structures is proposed. Transmission electron microscopy observation confirms the model predictions and reveals that the saturation state of relaxation is reached in the buried layers.

  • Work-hardening effects in the lattice relaxation of single lay er heterostructures
    D. González, D. Araújo, G. Aragón, and R. Garcı́a

    Applied Physics Letters, ISSN: 00036951, Pages: 2475-2477, Published: 27 October 1997 AIP Publishing
    A modelization of the strain relaxation in single heteroepitaxial layers is presented in this letter. The calculations consider the energetic variations of the heteroepitaxial structure when introducing one new dislocation into the existing interfacial array of fixed misfit dislocations without continuous readjustment of the spacing array. The interaction energy of the new dislocation with both lattice mismatch and dislocation array is shown to be the limiting factor that controls the mechanism of strain relaxation at the saturation stage of relaxation. The model is shown to be in good agreement with the lattice relaxation behavior of previously published strain/thickness data.

  • EBIC mode characterization of transport properties on laser heterostructures
    M.J. Romero, D. Araújo, J.D. Lambkin, and R. García

    Materials Science and Engineering B, ISSN: 09215107, Issue: 1-3, Pages: 57-60, Published: February 1997 Elsevier BV
    Abstract A method for the quantitative evaluation of electron-beam-induced current (EBIC) profiles across p-n junctions (normal-collector configuration) is presented. The procedure consists of firstly estimating the extent of electron-hole (e-h) pair generation by Monte Carlo calculations. Secondly, the steady-state diffusion equation is applied to minority carriers in each differential volume to evaluate the minority carrier collection probability. The model is then used to investigate (λ = 1.3 μm) InGaAsP/InP double bulk heterostructure lasers. From the comparison of experimental and calculated linescans, the minority carrier diffusion length and surface recombination velocity are evaluated to be L = 0.52 μm and S/D = 1 × 10 5 cm −1 at n-side and L = 0.87 μm and S/D = 5 × 10 4 cm −1 at p-side.

  • Advantages of thin interfaces in step-graded buffer structures
    D. González, D. Araújo, L. González, Y. González, G. Aragón, and R. García

    Materials Science and Engineering B, ISSN: 09215107, Issue: 1-3, Pages: 41-45, Published: February 1997 Elsevier BV
    Abstract The effect of graded interfaces in step-graded buffer structures on crystal relaxation efficiency is investigated by transmission electron microscopy and double crystal X-ray diffraction. A higher recombination rate leading to higher edge dislocation densities and a strong diminution of the tilt, is evidenced when graded interfaces are used. The latter feature is a consequence of the poor stability of dislocation multiplication sources in graded interfaces. The lower strain energy release of dislocation segments and a diminution of the pinning points in graded interfaces reduce the lifetime of dislocations sources, producing a better distribution of Burgers vector in the misfit dislocations array.

  • Energy-loss dependence of inelastic interactions between high-energy electrons and semiconductors: A model to determine the spatial distribution of electron-hole pairs generation
    M.J. Romero, D. Araújo, and R. García

    Materials Science and Engineering B, ISSN: 09215107, Issue: 1-3, Pages: 168-171, Published: 15 December 1996 Elsevier BV
    Abstract A scattering model to evaluate the extent of generated electron-hole pairs (e-h) in semiconductors during electron beam excitation in the 5-40 keV beam energy range is presented. From a modified Kanaya and Okayama model, the range R and energy-loss equation dE/dS dependence on the inelastic and elastic scattering cross-section proportion are analytically deduced, The presented model allows to modulate the proportion of inelastic-elastic scattering cross-section versus the energy of the incident electrons as occurs for each different interaction. Into this formalism is introduced the rate of Kα ionization events at different incident electron energy. This model is then used in Monte Carlo calculations to deduce the e-h generation function g(x, y, z) at different electron beam energy ( E b ) levels. As a result, both depth and lateral dependences of e-h generation are found to fit successfully the experimental distributions of Bonard et al. ( J. Appl. Phys., 79 (1996) 8693.

  • SCH laser recombination rate from EBIC profiles
    M.J. Romero, D. Araújo, and R. García

    Materials Science and Engineering B, ISSN: 09215107, Issue: 1-3, Pages: 172-175, Published: 15 December 1996 Elsevier BV
    Abstract A new method to evaluate the total recombination velocity R at the quantum wells (QW) using electron-beam-induced current (EBIC) linescans is presented. The procedure consists in, as a first step, estimating the electron-hole pairs (e-h) generation function g(x, y, z) applying Monte Carlo calculations where the incident electron energy dependence of the inelastic-elastic scattering cross-section proportion is introduced. Secondly, the steady-state diffusion equation is applied to minority carriers in each differential volume of e-h generation. This method is then used to investigate separate-confinement laser heterostructures (SCH). From the comparison between experimental and calculated EBIC linescans, minority carriers diffusion lengths at both sides of the laser junction and recombination rate in the active region are deduced. As a result, the recombination rate in the QWs of the laser structure is evaluated to be R ≈ 3 × 10 6 cm s −1 .

  • Cathodoluminescence study of the spatial distribution of electron-hole pairs generated by an electron beam in Al0.4Ga0.6As
    Jean‐Marc Bonard, Jean‐Daniel Ganière, Brigitte Akamatsu, Daniel Araújo, and Franz‐Karl Reinhart

    Journal of Applied Physics, ISSN: 00218979, Pages: 8693-8703, Published: 1 June 1996 AIP Publishing
    We use the cathodoluminescence mode of a scanning electron microscope to investigate the depth and lateral dependencies of the electron-hole pairs generation by the electron beam in Al0.4Ga0.6As semiconducting material. A multiquantum well structure acts as a detector to measure the relative number of generated minority carriers by their radiative recombination, allowing a direct assessment of the generation volume in the sample. In contrast to electron-beam induced current which was used in former studies, the method avoids the effect of carrier diffusion for direct band gap materials. This novel technique can be readily applied to other III-V and II-VI semiconductors. The results may be used for the quantitative interpretation of cathodoluminescence and electron-beam induced current measurements. (C) 1996 American Institute of Physics.

  • Dislocation behavior in InGaAs step- and alternating step-graded structures: Design rules for buffer fabrication
    D. Araújo, D. González, R. García, A. Sacedón, and E. Calleja

    Applied Physics Letters, ISSN: 00036951, Pages: 3632, Published: 1995 AIP Publishing
    A comparison between compositionally stepped and alternating step‐graded structures used in the production of a relaxation buffer layer is carried out by means of transmission electron microscopy. The latter shows higher efficiency in relieving the strain. A simple balance force model permits us to understand the reason for a higher generation of threading dislocations observed in the alternating step‐graded structures. The presented results can be applied as new design rules for buffer fabrication that contrast in some key points with previous published rules as, for example, the ‘‘zero‐net‐strain’’ precept [D. Dunstan, P. Kidd, P. F. Fewster, N. L. Andrew, L. Gonzalez, Y. Gonzalez, A. Sacedon, and F. Gonzalez‐Sanz, Appl. Phys. Lett. 65, 845 (1994)].

  • Design of InGaAs linear graded buffer structures
    A. Sacedón, F. González‐Sanz, E. Calleja, E. Muñoz, S. I. Molina, F. J. Pacheco, D. Araújo, R. García, M. Lourenço, Z. Yang, P. Kidd, and D. Dunstan

    Applied Physics Letters, ISSN: 00036951, Pages: 3334, Published: 1995 AIP Publishing
    The relaxation of compositionally graded InGaAs buffers, with and without uniform cap layers, has been studied. Simple InGaAs linear‐graded layers on GaAs substrates never reach complete relaxation. The residual strain in these structures produces a dislocation‐free strained top region while the rest of the buffer is nearly completely relaxed through misfit dislocations, as observed by transmission electron microscopy (TEM). This strained top region is analyzed and its thickness compared with theoretical calculations. The effects of different cap layers on the relaxation behavior of the graded buffer has been studied by double crystal x‐ray diffraction, TEM, and low temperature photoluminescence, and results compared with predictions of the models. The optical quality of the cap layer improves when its composition is close to the value that matches the lattice parameter of the strained surface of the grade. The design of linear graded buffers having a strain‐free cap layer with high crystalline quality is discussed.The relaxation of compositionally graded InGaAs buffers, with and without uniform cap layers, has been studied. Simple InGaAs linear‐graded layers on GaAs substrates never reach complete relaxation. The residual strain in these structures produces a dislocation‐free strained top region while the rest of the buffer is nearly completely relaxed through misfit dislocations, as observed by transmission electron microscopy (TEM). This strained top region is analyzed and its thickness compared with theoretical calculations. The effects of different cap layers on the relaxation behavior of the graded buffer has been studied by double crystal x‐ray diffraction, TEM, and low temperature photoluminescence, and results compared with predictions of the models. The optical quality of the cap layer improves when its composition is close to the value that matches the lattice parameter of the strained surface of the grade. The design of linear graded buffers having a strain‐free cap layer with high crystalline quality is...

  • Comparison of the lateral carrier transport between a GaAs single quantum well and the AlGaAs barrier during cathodoluminescence excitation
    D. Araújo, G. Oelgart, J.‐D. Ganière, and F. K. Reinhart

    Journal of Applied Physics, ISSN: 00218979, Pages: 342-346, Published: 1994 AIP Publishing
    In a recent paper we measured the lateral hole diffusion in a GaAs/AlGaAs single quantum well (SQW) by a novel method. At helium temperature, we estimate a lateral hole diffusion length in the QW of 1.5 μm. However, the assumption that diffusion takes place mainly in the SQW needs to be checked, as the measured diffusion length is the result of two competing processes: (i) hole diffusion in the SQW plane itself and (ii) hole diffusion in the barrier followed by recombination in the SQW. We present here a comparison between the lateral hole distribution in the SQW and in the AlGaAs barrier. First, we estimate the hole diffusion length in the barrier fitting experimental cathodoluminescence linescans on simulated ones. Second, using the measured diffusion lengths in the QW plane and in the bulk barrier and modeling the carrier transport, we deduce the lateral hole distribution in both layers. It is found that even for very large barriers (1.2 μm), the hole diffusion in the barrier contributes less than 0.1%...

  • One-step growth of buried heterostructures by chemical beam epitaxy over patterned InP substrates
    A. Rudra, H. Sugiura, J. Ling, J.M. Bonard, J.D. Ganière, M. de Fays, D. Araujo, and M. Ilegems

    Journal of Crystal Growth, ISSN: 00220248, Volume: 136, Issue: 1-4, Pages: 173-178, Published: 1 March 1994 Elsevier BV
    We studied the formation of buried heterostructures obtained in a single growth step over nonplanar substrates patterned with ridges. When the ridge dimensions are large enough, the growth on the mesa top is similar to that on a planar substrate. In contrast, ridge spacings below almost-equal-to 10 mum influence the composition of the alloys grown on the ridge as well as those grown in the valley centre. The possible surface mechanisms which may explain this behaviour are discussed.

  • Step-graded buffer layer study of the strain relaxation by transmission electron microscopy
    D. González, D. Araújo, S.I. Molina, A. Sacedón, E. Calleja, and R. García

    Materials Science and Engineering B, ISSN: 09215107, Issue: 1-3, Pages: 497-501, Published: December 1994 Elsevier BV
    Abstract The lattice relaxation behavior in an In x Ga 1−x As/GaAs linearly step-graded structure is studied by transmission electron microscopy (TEM). From the misfit dislocation densities measured by TEM at each interface the relaxation parameters such as strain and percentage relaxation are deduced for each layer. The obtained results are compared with the predictions of the Dunstan et al. model which describe the dislocation behavior during relaxation in such structures. A different relaxation behavior than that described by Dunstan et al. is observed. This is attributed to the fact that the individual layer thickness is lower than the critical layer thickness of Dunstan et al. Work-hardening processes are found to induce a linear increase in the residual strain with increasing layer thickness.

  • Determination of the lateral distribution of electron-hole pairs generated by an electron beam in Al0.4Ga0.6As by cathodoluminescence
    D. Araújo, J.-M. Bonard, G. Oelgart, J.-D. Ganière, F. Morier-Genoud, and F.-K. Reinhart

    Materials Science and Engineering B, ISSN: 09215107, Issue: 1-3, Pages: 124-129, Published: May 1994 Elsevier BV
    The cathodoluminescence mode of the scanning electron microscope is used for the first time to investigate the lateral dependence of the electron-hole pair generation by the electron beam of the scanning electron microscope m semiconducting material. A multiple-quantum-well structure acts as a detector to measure the relative number of generated carriers by their radiative recombination. The method, which avoids the effect of carrier diffusion, enhances the resolution of the measurement to 50 nm and should prove a help for the quantitative interpretation of cathodoluminescence evaluations.

  • Transmission electron microscopy study of InxGa1-xAs/GaAs multilayer buffer structures used as dislocation filters
    D. González, D. Araújo, A. Sacedón, E. Calleja, S.I. Molina, G. Aragón, and R. García

    Materials Science and Engineering B, ISSN: 09215107, Issue: 1-3, Pages: 515-519, Published: December 1994 Elsevier BV
    To investigate the efficiency of threading dislocation (TD) filtering in multilayer (ML) buffers, InxGa1-xAs/GaAs structures are studied by transmission electron microscopy. The TDs are generated at the first In0.3Ga0.7As thick layer. Different MLs harder and softer on average than this TD generator thick layer are used as filters. The efficiencies of the ML filters are compared with that of a bulk layer with identical average In content. As the individual ML thickness is below the Matthews-Blakeslee critical thickness, no TD bending should occur. However, in contrast with the softer buffer behavior, MLS buffer harder than the TD generator layer are shown to filter. This difference in the TD behavior between the two kinds of structure is attributed to yield strength effects. From a kinetic model, an expression for the TD density vs. the height is deduced. On application of this model to the measured TD densities, filtering parameters are deduced.

  • Strain relief in linearly graded composition buffer layers: A design scheme to grow dislocation-free (<105 cm-2) and unstrained epilayers
    S. I. Molina, F. J. Pacheco, D. Araújo, R. García, A. Sacedón, E. Calleja, Z. Yang, and P. Kidd

    Applied Physics Letters, ISSN: 00036951, Pages: 2460-2462, Published: 1994 AIP Publishing
    The strain relaxation in linearly graded composition InGaAs layers grown on (001) GaAs substrates by molecular beam epitaxy is studied by transmission electron microscopy (TEM) and double crystal x‐ray diffraction (DCXRD). The dislocation distribution in these layers does not coincide with the predicted equilibrium dislocation distribution [J. Tersoff, Appl. Phys. Lett. 62, 693 (1993)]. The dislocation density in the dislocation‐rich layer thickness is slightly smaller than the equilibrium density. The thickness of the dislocation‐rich region is different in the [110] and [110] directions. A good correspondence exists between the TEM and DCXRD strain measurements. The dislocation distribution observed by TEM has made it possible to design a scheme to grow dislocation‐free and unstrained top layers on linearly graded composition buffer layers.

  • Lateral transport in GaAs/AlGaAs quantum wells
    D. Araújo, G. Oelgart, J.‐D. Ganière, and F. K. Reinhart

    Applied Physics Letters, ISSN: 00036951, Pages: 2992-2994, Published: 1993 AIP Publishing
    The lateral transport of excess carriers in metal organic chemical vapor deposition grown GaAs/AlxGa1−xAs(x=0.5) 20 A thick single quantum well structures is studied by cathodoluminescence (CL) between 5 K≤T≤170 K. Impurity and native defect related transitions are found to take place around grown‐in dislocations where well thickness variations are also found. The CL intensity of free excitons and/or transitions involving impurities and native defects is measured as a function of distance from the dislocation to the point of excitation. Using a simple diffusion model, we are able to determine the hole diffusion length, L=1.5 μm, in slightly n‐doped SQW. This represents a novel method for the direct determination of the diffusion length in sufficiently defect‐free material.

  • Cathodoluminescence and photoluminescence studies of dislocations in GaAs/AlGaAs quantum wells
    D. Araújo, G. Oelgart, J.‐D. Ganière, and F. K. Reinhart

    Journal of Applied Physics, ISSN: 00218979, Pages: 1997-2003, Published: 1993 AIP Publishing
    The optical properties of low pressure metal organic vapor deposition grown GaAs/AlxGa1-xAs (x = 0.5) single quantum well structures (SQW) with grown-in dislocations (GD) were studied by low temperature cathodoluminescence (CL) and photoluminescence (PL). High luminescence efficiency around the GD was observed and attributed to impurity decoration. CL spectra show a region surrounding the GD that consists of Si impurities and native defects in the SQW and barrier layers. The diameter of this region was found to be in the order of 1 mum using spectrally resolved CL micrographs.

  • Chemical beam epitaxy of InP, InGaAs and InGaAsP on non-planar InP substrates
    H Sugiura, A Rudra, J F Carlin, H J Buhlmann, D Araujo, and M Ilegems

    Semiconductor Science and Technology, ISSN: 02681242, Pages: 1063-1068, Published: 1993 IOP Publishing
    The authors report the growth behavior of the InP, InGaAs and InGaAsP on non-planar InP substrates where ridges were formed with (111)A, (211)A, (111)B and (551) sidewall planes. All three materials grow uniformly on the whole patterned surface with (111)A and (211)A sidewall planes. They grow separately on the plateau and in the valley for the other two structures. The growth front of the InGaAs films is always rippled near the sidewalls, indicating large deviations from lattice-matched composition in these areas, while the growth front in the case of the InP and InGaAsP films remains smooth. Single-step growth of buried double heterostructures with a 1 mu m wide rib is realized for the structures with both (111)B and (551) sidewall planes. The growth mechanisms responsible for the observed features are discussed.

  • Self-interstitial mechanism for Zn diffusion-induced disordering of GaAs/AlxGa1-xAs (x=0.1-1) multiple-quantum-well structures
    Nguyen Hong Ky, J. D. Ganière, M. Gailhanou, B. Blanchard, L. Pavesi, G. Burri, D. Araújo, and F. K. Reinhart

    Journal of Applied Physics, ISSN: 00218979, Pages: 3769-3781, Published: 1993 AIP Publishing
    GaAs/AlxGa1−xAs multiple‐quantum‐well (MQW) structures with identical well thicknesses but with different Al contents x in the barrier (x≊0.1, 0.2, 0.45, and 1) were grown by molecular‐beam epitaxy to study the impurity‐induced disordering mechanism. The disordering of the structures is observed directly by transmission electron microscopy on cleaved wedges of the sample, by the secondary electron imaging mode of scanning electron microscopy, and by secondary‐ion‐mass spectroscopy after Zn diffusions at 575 °C during different times (1, 4, 9, and 16 h). The results show that the totally and partially disordered regions are always behind the Zn diffusion front. The partially disordered extent depends on x. As x increases, the disordering rate increases due to the increase in Zn diffusivity. The effect of high Zn concentration is investigated by photoluminescence and by Raman scattering measurements. The systematical analysis of the photoluminescence spectra of the MQW structures diffused for different time...

  • One step growth of buried heterostructures on non-planar InP substrates using chemical beam epitaxy
    1993 IEEE 5th International Conference on Indium Phosphide and Related Materials, Pages: 179-182, Published: 1993

  • Luminescence peculiarities on (AlGa)As single quantum well
    G. Oelgart, L. Lehmann, D. Araújo, J. D. Ganière, and F. K. Reinhart

    Journal of Applied Physics, ISSN: 00218979, Pages: 1552-1554, Published: 1992 AIP Publishing
    This paper reports on single quantum well characterization by means of luminescence excited with a laser (photoluminescence) and an electron beam (cathodoluminescence) at liquid helium temperatures. Small quantum well regions with smaller confinement were observed. They seem to be associated with dislocations originated at the substrate. The observed shift of the X (e-hh) peak position versus the excitation level can be explained by luminescence generation in different lateral regions of the quantum well.

  • Low‐Temperature EBIC Study of Zn‐Diffused GaAs p‐n Junctions
    D. Araújo, L. Pavesi, Nguyen Hong Ky, J.-D. Ganière, and F. K. Reinhart

    physica status solidi (a), ISSN: 00318965, eISSN: 1521396X, Volume: 129, Pages: 555-567, Published: 16 February 1992 Wiley
    To study the effect of damage induced during the Zn diffusion on the properties of the material, p-n junctions, obtained by zinc diffusion, are investigated by electron beam induced current (EBIC) at different temperatures. At helium temperature, the EBIC decay on the p-side is flattened and non exponential. This effect is attributed to the defects induced by the Zn-diffusion that act as non-radiative centers. The room temperature EBIC signal has a symmetric exponential decay on both sides of the junction. The EBIC measurements for different temperatures and electron beam voltages indicate that the surface recombinations affect the carrier transport at room temperature hindering the non-exponential EBIC decay observed at helium temperature. The recombination dynamic is affected stronger by the as grown (001) surface than by the cleaved (110) surface.

  • Cathodoluminescence study of oval defects on QW structures
    Institute of Physics Conference Series, ISSN: 03730751, Issue: 117, Pages: 703-706, Published: 1991

  • Thermal conversion of n-type GaAs:Si to p type in excess arsenic vapor
    Nguyen Hong Ky, L. Pavesi, D. Araújo, J. D. Ganière, and F. K. Reinhart

    Journal of Applied Physics, ISSN: 00218979, Pages: 3887-3891, Published: 1991 AIP Publishing
    Annealing in excess arsenic vapor at 650 °C introduces thermal conversion of n‐type Si‐doped GaAs samples (n = 1.3 × 1018 cm−3) into p type. The observations are made by current‐voltage and electron‐beam induced current measurements. The donor concentration on the n side near the junction decreases after annealing. We present a comparison between the photoluminescence spectra of samples annealed under different conditions and an analysis of depth profile of the photoluminescence spectra. Our results underline the important role of gallium vacancies and gallium vacancy‐silicon donor complex in the thermal conversion.

  • A model for the zn diffusion in gaas by a photoluminescence study
    Nguyen Hong Ky, L. Pavesi, D. Araújo, J. D. Ganière, and F. K. Reinhart

    Journal of Applied Physics, ISSN: 00218979, Pages: 7585-7593, Published: 1991 AIP Publishing
    To study the mechanism of zinc diffusion in GaAs, we diffused zinc from a ZnAs2 source into Si‐doped GaAs samples (n ≊ 1.3 × 1018 cm−3) at different temperatures (from 575 °C up to 700 °C) in sealed evacuated quartz tubes. The samples are characterized by the depth profile of the photoluminescence at different temperatures. The photoluminescence spectra show characteristic emission associated to deep levels of gallium and arsenic vacancies. A detailed analysis of the spectra demonstrates the role played by vacancies in the Zn diffusion process. The spatial correlation between the luminescence spectra and the Zn concentration obtained from secondary ion mass spectroscopy measurements has been demonstrated.

  • Zinc diffusion in GaAs and zinc-induced disordering of GaAs/AlGaAs multiple quantum wells: a multitechnique study
    L. Pavesi, D. Araujo, Nguyen Hong Ky, J. D. Gani�re, F. K. Reinhart, P. A. Buffat, and G. Burri

    Optical and Quantum Electronics, ISSN: 03068919, eISSN: 1572817X, Published: January 1991 Springer Science and Business Media LLC
    A review of experimental results obtained by different techniques is presented on the problem of zinc diffusion. Zinc diffusion was carried out on Si-doped GaAs (n≈1018 cm−3) and on multiple quantum well (MQW) structures. The samples were investigated by secondary-ion mass spectroscopy (SIMS), different imaging modes of scanning electron microscopy such as secondary electrons, cathodoluminescence (CL) and electron beam-induced current (EBIC), transmission electron microscopy on a wedge-shaped specimen (WTEM) and by photoluminescence (PL). A nonexponential decay of the low-temperature EBIC signal accompanied by a very low CL signal due to the high density of nonradiative recombination centres were observed in the diffused region of the n-doped GaAs. Indeed, PL measurements demonstrate that Ga vacancies play a key role on the mechanism of the Zn diffusion. On the impurity-induced disordered (IID) MQW samples, an enrichment of Al at the surface was observed by SIMS and confirmed by WTEM and PL. Low-temperature PL spectra show the gradual disappearance of the MQW excitonic transitions as the number of disordered layers increases. When all of the MQW structure is destroyed, the band-to-band recombinations in the IID produced alloy dominate the PL spectrum.

RECENT SCHOLAR PUBLICATIONS

  • Lattice performance during initial steps of the Smart-Cut™ process in semiconducting diamond: A STEM study
    JC Piero, J de Vecchy, D Fernndez, G Alba, J Widiez, L Di Cioccio, ...
    Applied Surface Science 528, 146998 2020

  • Impact of Methane Concentration on Surface Morphology and Boron Incorporation of Heavily Boron-doped Single Crystal Diamond Layers
    R Rouzbahani, SS Nicley, DEP Vanpoucke, F Lloret, P Pobedinskas, ...
    Carbon 2020

  • Comprehensive nanoscopic analysis of tungsten carbide/Oxygenateddiamond contacts for Schottky barrier diodes
    DA G. Albaa, D. Leinen, M.P. Villar, R. Alcntara, J.C. Piero, A. Fiori, T ...
    Applied surface science 537, 147874 2020

  • Analysis by HR-STEM of the Strain Generation in InP after SiN x Deposition and ICP Etching
    M Gutirrez, DF Reyes, D Araujo, JP Landesman, E Pargon
    Journal of Electronic Materials 49 (9), 5226-5231 2020

  • Study of Early Stages in the Growth of Boron‐Doped Diamond on Carbon Fibers
    J Milln-Barba, M Gutirrez, F Lloret, RG de Villoria, R Alcntara, ...
    physica status solidi (a), 2000284 2020

  • Interfacial integrity enhancement of atomic layer deposited alumina on boron doped diamond by surface plasma functionalization
    A Jaggernauth, RM Silva, MA Neto, FJ Oliveira, IK Bdikin, MP Alegre, ...
    Surface and Coatings Technology, 125991 2020

  • Surface States of (100) O-Terminated Diamond: Towards Other 1 1: O Reconstruction Models
    G Alba, MP Villar, R Alcntara, J Navas, D Araujo
    Nanomaterials 10 (6), 1193 2020

  • Diamond/γ-alumina band offset determination by XPS
    J Caas, G Alba, D Leinen, F Lloret, M Gutierrez, D Eon, J Pernot, ...
    Applied Surface Science, 146301 2020

  • H-Terminated Diamond Surface Band Bending Characterization by Angle-Resolved XPS
    G Alba, D Eon, MP Villar, R Alcntara, G Chicot, J Caas, J Letellier, ...
    Surfaces 3 (1), 61-71 2020

  • How to Grow Fully (100) Oriented SiC/Si/SiC/Si Multi‐Stack
    T Yeghoyan, K Alassaad, V Soulire, G Ferro, M Gutierrez, D Araujo
    physica status solidi (a) 216 (10), 1800588 2019

  • How to Grow Fully (100) Oriented SiC/Si/SiC/Si Multi‐Stack
    T Yeghoyan, K Alassaad, V Soulire, G Ferro, M Gutierrez, D Araujo
    physica status solidi (a) 216 (10), 1800588 2019

  • High resolution boron content profilometry at δ-doping epitaxial diamond interfaces by CTEM
    JC Pinero, F Lloret, MP Alegre, MP Villar, A Fiori, E Bustarret, D Arajo
    Applied Surface Science 461, 221-226 2018

  • Determination of alumina bandgap and dielectric functions of diamond MOS by STEM-VEELS
    J Caas, JC Piero, F Lloret, M Gutierrez, T Pham, J Pernot, D Araujo
    Applied Surface Science 461, 93-97 2018

  • Calibration of a Cohesive Model for Fracture in Low Cross-Linked Epoxy Resins
    D Torres, S Guo, MP Villar, D Araujo, R Estevez
    Polymers 10 (12), 1321 2018

  • Three-Dimensional Diamond MPCVD Growth over MESA Structures: A Geometric Model for Growth Sector Configuration
    F Lloret, D Araújo, D Eon, E Bustarret
    Crystal Growth & Design 18 (12), 7628-7632 2018

  • Crystalline Defects Induced during MPCVD Lateral Homoepitaxial Diamond Growth
    F Lloret, D Eon, E Bustarret, D Araujo
    Nanomaterials 8 (10), 814 2018

  • GaSb and GaSb/AlSb Superlattice Buffer Layers for High-Quality Photodiodes Grown on Commercial GaAs and Si Substrates
    M Gutirrez, F Lloret, P Jurczak, J Wu, HY Liu, D Arajo
    Journal of Electronic Materials 47 (9), 5083-5086 2018

  • Control of the Alumina Microstructure to Reduce Gate Leaks in Diamond MOSFETs
    M Gutirrez, F Lloret, TT Pham, J Caas, DF Reyes, D Eon, J Pernot, ...
    Nanomaterials 8 (8), 584 2018

  • Boron-Doping Proximity Effects on Dislocation Generation during Non-Planar MPCVD Homoepitaxial Diamond Growth
    F Lloret, D Eon, E Bustarret, A Fiori, D Araujo
    Nanomaterials 8 (7), 480 2018

  • 5.1. 3 Metal oxide semiconductor interface and transmission electron microscopy characterization
    D Araujo, J Pernot
    Power Electronics Device Applications of Diamond Semiconductors, 323-46 2018

MOST CITED SCHOLAR PUBLICATIONS

  • Microstructural study of CO2 laser machined heat affected zone of 2024 aluminum alloy
    D Araujo, FJ Carpio, D Mendez, AJ Garcıa, MP Villar, R Garcıa, ...
    Applied surface science 208, 210-217 2003
    Citations: 75

  • Design of InGaAs linear graded buffer structures
    A Sacedon, F Gonzlez‐Sanz, E Calleja, E Munoz, SI Molina, FJ Pacheco, ...
    Applied physics letters 66 (24), 3334-3336 1995
    Citations: 75

  • A model for the Zn diffusion in GaAs by a photoluminescence study
    NH Ky, L Pavesi, D Araujo, JD Ganiere, FK Reinhart
    Journal of applied physics 69 (11), 7585-7593 1991
    Citations: 69

  • Optimization of AlN thin layers on diamond substrates for high frequency SAW resonators
    JG Rodrguez-Madrid, GF Iriarte, D Araujo, MP Villar, OA Williams, ...
    Materials Letters 66 (1), 339-342 2012
    Citations: 50

  • Study of isolated cubic GaN quantum dots by low-temperature cathodoluminescence
    JP Garayt, JM Gerard, F Enjalbert, L Ferlazzo, S Founta, ...
    Physica E: Low-dimensional Systems and Nanostructures 26 (1-4), 203-206 2005
    Citations: 48

  • Strain relief in linearly graded composition buffer layers: A design scheme to grow dislocation‐free (<105 cm−2) and unstrained epilayers
    SI Molina, FJ Pacheco, D Araujo, R Garcia, A Sacedon, E Calleja, Z Yang, ...
    Applied physics letters 65 (19), 2460-2462 1994
    Citations: 48

  • Hole transport in boron delta-doped diamond structures
    G Chicot, TN Tran Thi, A Fiori, F Jomard, E Gheeraert, E Bustarret, ...
    Applied Physics Letters 101 (16), 162101 2012
    Citations: 42

  • Nucleation of InN quantum dots on GaN by metalorganic vapor phase epitaxy
    JG Lozano, AM Snchez, R Garca, D Gonzlez, D Arajo, S Ruffenach, ...
    Applied Physics Letters 87 (26), 263104 2005
    Citations: 35

  • Self‐interstitial mechanism for Zn diffusion‐induced disordering of GaAs/AlxGa1−xAs (x=0.1−1) multiple‐quantum‐well structures
    NH Ky, JD Ganiere, M Gailhanou, B Blanchard, L Pavesi, G Burri, ...
    Journal of applied physics 73 (8), 3769-3781 1993
    Citations: 34

  • Correlation of optical and photoluminescence properties in amorphous SiNx: H thin films deposited by PECVD or UVCVD
    JF Lelivre, J De la Torre, A Kaminski, G Bremond, M Lemiti, ...
    Thin Solid Films 511, 103-107 2006
    Citations: 33

  • Cathodoluminescence study of the spatial distribution of electron‐hole pairs generated by an electron beam in Al0.4Ga0.6As
    JM Bonard, JD Ganire, B Akamatsu, D Arajo, FK Reinhart
    Journal of applied physics 79 (11), 8693-8703 1996
    Citations: 33

  • Electronic and physico-chemical properties of nanometric boron delta-doped diamond structures
    G Chicot, A Fiori, PN Volpe, TN Tran Thi, JC Gerbedoen, J Bousquet, ...
    Journal of applied physics 116 (8), 083702 2014
    Citations: 30

  • Homoepitaxial {111}‐oriented diamond pn junctions grown on B‐doped Ib synthetic diamond
    A Tajani, C Tavares, M Wade, C Baron, E Gheeraert, E Bustarret, ...
    physica status solidi (a) 201 (11), 2462-2466 2004
    Citations: 29

  • Fatigue behaviour of laser machined 2024 T3 aeronautic aluminium alloy
    FJ Carpio, D Arajo, FJ Pacheco, D Mndez, AJ Garcı́a, MP Villar, ...
    Applied Surface Science 208, 194-198 2003
    Citations: 29

  • Spatially correlated microstructure and superconductivity in polycrystalline boron-doped diamond
    F Dahlem, P Achatz, OA Williams, D Araujo, E Bustarret, H Courtois
    Physical Review B 82 (3), 033306 2010
    Citations: 26

  • Effect of oxygen on the cathodoluminescence signal from excitons, impurities and structural defects in homoepitaxial (100) diamond films
    M Kadri, D Araujo, M Wade, A Deneuville, E Bustarret
    Diamond and related materials 14 (3-7), 566-569 2005
    Citations: 26

  • Improved depth resolution of secondary ion mass spectrometry profiles in diamond: A quantitative analysis of the delta-doping
    A Fiori, F Jomard, T Teraji, G Chicot, E Bustarret
    Thin Solid Films 557, 222-226 2014
    Citations: 25

  • Critical boron-doping levels for generation of dislocations in synthetic diamond
    MP Alegre, D Araujo, A Fiori, JC Pinero, F Lloret, MP Villar, P Achatz, ...
    Applied Physics Letters 105 (17), 173103 2014
    Citations: 22

  • SiC voids, mosaic microstructure and dislocations distribution in Si carbonized layers
    FM Morales, SI Molina, D Araujo, R Garcı́a, V Cimalla, J Pezoldt
    Diamond and related materials 12 (3-7), 1227-1230 2003
    Citations: 21

  • Dislocation behavior in InGaAs step‐and alternating step‐graded structures: Design rules for buffer fabrication
    D Araujo, D Gonzalez, R Garcia, A Sacedon, E Calleja
    Applied physics letters 67 (24), 3632-3634 1995
    Citations: 21

GRANT DETAILS

1-. Nuevas aleaciones de carbono semiconductoras para una nueva generación de dispositivos electrónicos (CARBOTRONICS-PUENTE)
Universidad de Cádiz (Puerto Real, Cádiz)2020-04 hasta 2021-03|
GRANT_NUMBER: Ref: FEDER-UCA18-106470

2-. Composite de Fibra de carbono (CFRP) conductor térmico y eléctrico por percolación de nano-diamantes (Carbo-Diam)
Junta de Andalucía (Sevilla, Andalucia)2020-02 hasta 2022-01|
GRANT_NUMBER: sol-201800107851-tra

3-. Composite de Fibra de carbono (CFRP) conductor térmico y eléctrico por percolación de nano-diamantes (Carbo-Diam)
Consejería de Economía y Conocimiento. Junta de Andalucía (Sevialla, Andalucía)2019-12 hasta 2022-12|
GRANT_NUMBER: Ref: FDER-UCA-18-107851

4-. Nuevas aleaciones de carbono semiconductoras para una nueva generación de dispositivos electrónicos (CARBOTRONICS-PUENTE)
Consejería de Economía y Conocimeinto. Junta de Andalucía (Sevilla, Andalucía)2019-12 hasta 2021|
GRANT_NUMBER: Ref: FEDER-UCA-18-106586

5-. Fibras de carbono recubiertas de diamante, la nueva generación de composites (CFRP)
Ministerio de Ciencia e Innovación (Cádiz, Andalucía)2018-11 hasta 2020-10|
GRANT_NUMBER: ESP2017 91820 EXP

6-. Architectura 3D de mosfet elaborada in-situ por MPCVD para electrónica de potencia
Ministerio de Economía, Industria y Competitividad, Gobierno de España (Cádiz, Andalucía)2018-01 hasta 2020-12|
GRANT_NUMBER: TEC2017-86347-C2-1-R

7-. Mejora de las prestaciones del laboratorio de preparación de muestras para microscopías (LPM) de los servicios centrales de investigación científica y tecnológica de la universidad de cádiz
Unión Europea (Cádiz, Andalucía)2016-01 hasta 2017-12|Adjudicación
GRANT_NUMBER: UNCA15-CE3256

8-. Green electronics with diamond power devices
European Commission Horizon 2020 (Cádiz, Andalucía)2015-05 hasta 2019-04|Adjudicación
GRANT_NUMBER: SEP-2010-039524

INDUSTRY EXPERIENCE

1-. IBM research center : Zürich, Cantón de Zürich, CH
1992-09-15 hasta 1993-01-15 | Researcher (IBM research center)Employment

2-. Nestec S.A.: Lausanne, Cantón de Vaud, CH
1986-09-02 hasta 1987-08-31 | Researcher (Physics Department)Employment