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1. Experimental Characterization of Temperature-Dependent Microwave Noise of Discrete HEMTs: Drain Noise and Real-Space Transfer

   https://doi.org/10.1109/IMS37962.2022.9865505  

   Gabritchidze, Bekari; Cleary, Kieran; Kooi, Jacob; Esho, Iretomiwa; Readhead, Anthony C.; Minnich, Austin J. (June 2022, 2022 IEEE/MTT-S International Microwave Symposium - IMS 2022)

   We report wafer characterization of the S-parameters and microwave noise temperature of discrete GaAs and GaN HEMTs over a temperature range of 20 - 300 K. The measured noise temperature (T50) exhibits a dependence on physical temperature that is inconsistent with a constant drain temperature, with Td for the GaAs and GaN devices changing from ~ 2000 K and ~2800 K at room temperature to ~ 700 K and ~ 1800 K at cryogenic temperatures, respectively. The observed temperature dependence is qualitatively consistent with that predicted from a theory of drain noise based on real-space transfer of electrons from the channel to the barrier. 

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2. Dual Protection Layer Strategy to Increase Photoelectrode–Catalyst Interfacial Stability: A Case Study on Black Silicon Photoelectrodes

   Fan, Y.; Aguiar, J.A.; Fairchild, M.; Vakki, W.; Younan, S.; Zhou, Y.H.; Zhuo, L.H.; Gu, J.* (April 2019, Advanced materials interfaces)

   Photoelectrode degradation under harsh solution conditions continues to be a major hurdle for long-term operation and large-scale implementation of solar fuel conversion. In this study, a dual-layer TiO2 protection strategy is presented to improve the interfacial durability between nanoporous black silicon and photocatalysts. Nanoporous silicon photocathodes decorated with catalysts are passivated twice, providing an intermediate TiO2 layer between the substrate and catalyst and an additional TiO2 layer on top of the catalysts. Atomic layer deposition of TiO2 ensures uniform coverage of both the nanoporous silicon substrate and the catalysts. After 24 h of electrolysis at pH = 0.3, unprotected photocathodes layered with platinum and molybdenum sulfide retain only 30% and 20% of their photocurrent, respectively. At the same pH, photocathodes layered with TiO2 experience an increase in photocurrent retention: 85% for platinum-coated photocathodes and 91% for molybdenum sulfide–coated photocathodes. Under alkaline conditions, unprotected photocathodes experience a 95% loss in photocurrent within the first 4 h of electrolysis. In contrast, TiO2-protected photocathodes maintain 70% of their photocurrent during 12 h of electrolysis. This approach is quite general and may be employed as a protection strategy for a variety of photoabsorber–catalyst interfaces under both acidic and basic electrolyte conditions 

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3. Improved Lifetime of GaN-Based Single Phase PV Inverter Using Dynamic Hardware Allocation

   https://doi.org/10.1109/ECCE47101.2021.9595850  

   Sabi, Kamal; Costinett, Daniel (October 2021, 2021 IEEE Energy Conversion Congress and Exposition (ECCE))

   Power electronic inverters for photovoltaic (PV) systems over the years have trended towards high efficiency and power density. However, reliability improvements of inverters have received less attention. Inverters are one of the lifetime-limiting elements in most PV systems. Their failures increase system operation and maintenance costs, contributing to an increased lifetime energy cost of the PV system. Opportunities exist to increase inverter reliability through design for reliability techniques and the use of new modular topologies, semiconductor devices, and energy buffering schemes. This paper presents the implementation and design for reliability for a GaN-based single-phase residential string inverter using a new topological and control scheme that allows dynamic hardware allocation (DHA). In the proposed inverter architecture, a range of identical modules and control schemes are used to dispatch hardware resources within the inverter to variably deliver power to the load or filter the second harmonic current on the DC side. This new approach more than triples the lifetime of GaN-based inverters, reducing system repair/replacement costs, and increasing the PV system lifetime energy production. 

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4. Efficient on-chip terahertz generation and detection with GaN photoconductive emitters

   https://doi.org/10.1038/s41377-025-01870-6  

   Uzundal, Can_B; Feng, Qixin; Tang, Weichen; Hu, Chen; Sanborn, Collin; Yoon, Yoseob; Chen, Sudi; Ruan, Jiawei; Louie, Steven_G; Wang, Feng (June 2025, Light: Science & Applications)

   Abstract Photoconductive emitters for terahertz generation hold promise for highly efficient down-conversion of optical photons because it is not constrained by the Manley-Rowe relation. Existing terahertz photoconductive devices, however, faces limits in efficiency due to the semiconductor properties of commonly used GaAs materials. Here, we demonstrate that large bandgap semiconductor GaN, characterized by its high breakdown electric field, facilitates the highly efficient generation of terahertz waves in a coplanar stripline waveguide. Towards this goal, we investigated the excitonic contribution to the electro-optic response of GaN under static electric field both through experiments and first-principles calculations, revealing a robust excitonic Stark shift. Using this electro-optic effect, we developed a novel ultraviolet pump-probe spectroscopy for in-situ characterization of the terahertz electric field strength generated by the GaN photoconductive emitter. Our findings show that terahertz power scales quadratically with optical excitation power and applied electric field over a broad parameter range. We achieved an optical-to-terahertz conversion efficiency approaching 100% within the 0.03–1 THz bandwidth at the highest bias field (116 kV/cm) in our experiment. Further optimization of GaN-based terahertz generation devices could achieve even greater optical-to-terahertz conversion efficiencies. 

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5. 2023 IEEE Energy Conversion Congress and Exposition (ECCE)

   https://doi.org/10.1109/ECCE53617.2023  

   Sayed, Hussain; Krishnamoorthy, Harish (January 2023, IEEE)

   This paper presents an improved on-state resistance (RDSon) measurement scheme for high and low-side GaN FETs, which is critical for reliable and precise assessment of GaN HEMT power devices’ lifetime and degradation patterns. The proposed circuit is based on an active voltage clamp using Si MOSFET and Schottky and Zener diodes. The proposed circuit features lower parasitic inductances and capacitances by replacing the Si MOSFET with e-mode GaN FET. This modification contributed to much lower ringing and spikes in the voltage and current waveform of both the measurement FET and the DUT. The absence of an embedded body diode in the GaN device in the measurement circuit allows zero reverse recovery operation, making it more viable in high-frequency power converters. This study also provides a detailed design analysis of a bootstrap GaN-based on-state voltage (VDSon) sensing scheme for high-side FETs, useful in multiple converter configurations for in-situ devices’ health monitoring and conditioning. Simulation and experimental results validate the performance and features of the proposed concepts. 

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