Bottom-Up Formation of III-Nitride Nanowires: Past, Present, and Future for Photonic Devices Jungwook Min, Yue Wang, Tae‐Yong Park, Danhao Wang, Bilal Janjua, et al. Advanced Materials, 2024 The realization of semiconductor heterostructures marks a significant advancement beyond silicon technology, driving progress in high‐performance optoelectronics and photonics, including high‐brightness light emitters, optical communication, and quantum technologies. In less than a decade since 1997, nanowires research has expanded into new application‐driven areas, highlighting a significant shift toward more challenging and exploratory research avenues. It is therefore essential to reflect on the past motivations for nanowires development, and explore the new opportunities it can enable. The advancement of heterogeneous integration using dissimilar substrates, materials, and nanowires‐semiconductor/electrolyte operating platforms is ushering in new research frontiers, including the development of perovskite‐embedded solar cells, photoelectrochemical (PEC) analog and digital photonic systems, such as PEC‐based photodetectors and logic circuits, as well as quantum elements, such as single‐photon emitters and detectors. This review offers rejuvenating perspectives on the progress of these group‐III nitride nanowires, aiming to highlight the continuity of research toward high impact, use‐inspired research directions in photonics and optoelectronics.
Improving the Thermal Management of Power LED Arrays with Diamond Shusmitha Kyatam, Antonio A. Marques, Luis N. Alves, Luis Rodrigues, Joana C. Mendes 2024 IEEE 10th Electronics System Integration Technology Conference Estc 2024 Proceedings, 2024 The continuous increase of power density levels in components such as RF HEMTs or power LEDs and SiPs often leads to elevated hotspot temperatures that bring along reliability issues. Extracting and transferring the heat from the hotspot to the package and heatsink is however becoming increasingly difficult. One possible solution is the integration of materials with high thermal conductivity at package or board levels. Artificial diamond manufactured by chemical vapor deposition can have a thermal conductivity as high as 1800 W/m-K., a value 4.5 times higher than Cu. In this work we evaluate the potential of mounting several LEDs on diamond boards. To this end, the thermal profile of a $2\\times 2$ array of Cree XLamp XB-D LEDs mounted on MCPCBs and diamond boards was evaluated using Ansys. The impact of replacing the AIN die-carrier in the LED package with diamond was also evaluated. Due to the low thermal conductivity of the MCPCB dielectric layer, replacing the board with diamond has a larger impact than replacing the AIN die-carrier. The thermal benefit of diamond increases as thermal power density rises, either by increasing current levels or by bringing the LEDs closer to one another - even though replacing the MCPCB with a diamond board may induce thermal cross-talk between individual LEDs. By replacing both die-carrier and MCPCB with diamond, for 700 mA the aging of the LEDs slows down $\\approx$ 79-97% depending on the activation energy of the failure mechanisms. Further benefit can be obtained by using die-attach, solders and thermal interface materials and solders with high thermal conductivity.
Diamond coated fiber optic interferometric sensors: fabrication and application Shusmitha Kyatam, Ricardo Oliveira, Ana M. Rocha, Debarati Mukherjee, Miguel A. Neto, et al. Optical Materials Express, 2023 Diamond films were deposited by chemical vapor deposition (CVD) on the tip of Fabry-Perot (FPI) and multi-mode (MMI) optical fiber interferometers. Diamond provides a robust interface capable of forming covalent bonds between atoms on its surface and receptor molecules, required for biosensing applications. The films were characterized by optical and scanning electron microscopy (SEM), optical profilometry and Raman spectroscopy. The diamond-coated interferometers were tested with different refractive index solutions. The sensors response was 40 ± 1 dB/RIU and −987 ± 70 pm/ RIU for the FPI and −11 ± 1 dB/RIU for the MMI.
A Simple Method to Extract the Thermal Resistance of GaN HEMTs From De-Trapping Characteristics Benito González, Luís C. Nunes, Jo ao L. Gomes, Joana C. Mendes, Jose L. Jimenez IEEE Electron Device Letters, 2023 This letter proposes a new method for extracting the thermal resistance of GaN-based HEMTs using pulse recovery data. After the device temperature and trapping state are established from different quiescent power dissipations for several base-plate temperatures, the recovery profile of the drain current is measured. The recovery time is then used as a temperature-sensitive electrical parameter to extract the thermal resistance of the device. The proposed method has been applied to a Schottky-gate HEMT on SiC, for which a thermal resistance of 15.7 °C-mm/W was extracted, a value in good agreement with others reported for similar devices. Comparison with the one obtained from a step response is also done. Finally, the uncertainties of the proposed method related to the pulse width, temperature, percentage of the drain current recovery time, and averaging procedure are discussed.
Modeling temperature dynamic effects for high-power light-emitting diodes Shusmitha Kyatam, Luis Rodrigues, Luis N. Alves, Stanislav I. Maslovski, Joana C. Mendes International Journal of Circuit Theory and Applications, 2023 SummaryTemperature is a dynamic variable in most electronic devices. As the device operates, it generates heat, which translates in a temperature increase. Available models commonly disregard these variations due to the fact that they manifest at very large time scales. However, temperature dynamic effects have profound implications on the device model and on our common understanding. This paper discusses implications of considering the temperature variations on the current–voltage characteristic curves of power light‐emitting diodes. The main theoretical results establish that the current equation has a memristive nature when temperature is assumed as a dynamical state variable. This hypothesis is then validated experimentally.
The Gemstone Cyborg: How Diamond Films Are Creating New Platforms for Cell Regeneration and Biointerfacing Nádia E. Santos, Joana C. Mendes, Susana Santos Braga Molecules, 2023 Diamond is a promising material for the biomedical field, mainly due to its set of characteristics such as biocompatibility, strength, and electrical conductivity. Diamond can be synthesised in the laboratory by different methods, is available in the form of plates or films deposited on foreign substrates, and its morphology varies from microcrystalline diamond to ultrananocrystalline diamond. In this review, we summarise some of the most relevant studies regarding the adhesion of cells onto diamond surfaces, the consequent cell growth, and, in some very interesting cases, the differentiation of cells into neurons and oligodendrocytes. We discuss how different morphologies can affect cell adhesion and how surface termination can influence the surface hydrophilicity and consequent attachment of adherent proteins. At the end of the review, we present a brief perspective on how the results from cell adhesion and biocompatibility can make way for the use of diamond as biointerface.
