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1. Experimental Investigation of Drain Noise in High Electron Mobility Transistors: Thermal and Hot Electron Noise

   https://doi.org/10.1109/TED.2024.3445889  

   Gabritchidze, Bekari; Chen, Justin H; Cleary, Kieran A; Readhead, Anthony C; Minnich, Austin J (October 2024, IEEE Transactions on Electron Devices)

   e report the on-wafer characterization of S-parameters and microwave noise temperature (T50) of discrete metamorphic InGaAs high electron mobility transistors (mHEMTs) at 40 and 300 K and over a range of drain-source voltages (VDS). From these data, we extract a small-signal model (SSM) and the drain (output) noise current power spectral density (Sid) at each bias and temperature. This procedure enables Sid to be obtained while accounting for the variation of SSM, noise impedance match, and other parameters under the various conditions. We find that the noise associated with the channel conductance can only account for a portion of the measured output noise. Considering the variation of output noise with physical temperature and bias and prior studies of microwave noise in quantum wells, we hypothesize that a hot electron noise source (NS) based on real-space transfer (RST) of electrons from the channel to the barrier could account for the remaining portion of Sid. We suggest further studies to gain insights into the physical mechanisms. Finally, we calculate that the minimum HEMT noise temperature could be reduced by up to ∼50% and ∼30% at cryogenic temperature and room temperature, respectively, if the hot electron noise were suppressed. 

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2. Theory of drain noise in high electron mobility transistors based on real-space transfer

   https://doi.org/10.1063/5.0069352  

   Esho, Iretomiwa; Choi, Alexander Y.; Minnich, Austin J. (February 2022, Journal of Applied Physics)

   High electron mobility transistors are widely used as microwave amplifiers owing to their low microwave noise figure. Electronic noise in these devices is typically modeled by noise sources at the gate and drain. While consensus exists regarding the origin of the gate noise, that of drain noise is a topic of debate. Here, we report a theory of drain noise as a type of partition noise arising from real-space transfer of hot electrons from the channel to the barrier. The theory accounts for the magnitude and dependencies of the drain temperature and suggests strategies to realize devices with lower noise figure. 

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3. Self-heating of cryogenic high electron-mobility transistor amplifiers and the limits of microwave noise performance

   https://doi.org/10.1063/5.0103156  

   Ardizzi, Anthony J.; Choi, Alexander Y.; Gabritchidze, Bekari; Kooi, Jacob; Cleary, Kieran A.; Readhead, Anthony C.; Minnich, Austin J. (August 2022, Journal of Applied Physics)

   The fundamental limits of the microwave noise performance of high electron-mobility transistors (HEMTs) are of scientific and practical interest for applications in radio astronomy and quantum computing. Self-heating at cryogenic temperatures has been reported to be a limiting mechanism for the noise, but cryogenic cooling strategies to mitigate it, for instance, using liquid cryogens, have not been evaluated. Here, we report microwave noise measurements of a packaged two-stage amplifier with GaAs metamorphic HEMTs immersed in normal and superfluid [Formula: see text]He baths and in vacuum from 1.6 to 80 K. We find that these liquid cryogens are unable to mitigate the thermal noise associated with self-heating. Considering this finding, we examine the implications for the lower bounds of cryogenic noise performance in HEMTs. Our analysis supports the general design principle for cryogenic HEMTs of maximizing gain at the lowest possible power. 

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4. Ensemble GaAsSb/GaAs axial configured nanowire-based separate absorption, charge, and multiplication avalanche near-infrared photodetectors

   https://doi.org/10.1039/D2NA00359G  

   Parakh, M.; Pokharel, R.; Dawkins, K.; Devkota, S.; Li, J.; Iyer, S. (January 2022, Nanoscale Advances)

   In this study, molecular beam epitaxially grown axially configured ensemble GaAsSb/GaAs separate absorption, charge, and multiplication (SACM) region-based nanowire avalanche photodetector device on non-patterned Si substrate is presented. Our device exhibits a low breakdown voltage ( V BR ) of ∼ −10 ± 2.5 V under dark, photocurrent gain ( M ) varying from 20 in linear mode to avalanche gain of 700 at V BR at a 1.064 μm wavelength. Positive temperature dependence of breakdown voltage ∼ 12.6 mV K −1 further affirms avalanche breakdown as the gain mechanism in our SACM NW APDs. Capacitance–voltage ( C – V ) and temperature-dependent noise characteristics also validated punch-through voltage ascertained from I – V measurements, and avalanche being the dominant gain mechanism in the APDs. The ensemble SACM NW APD device demonstrated a broad spectral room temperature response with a cut-off wavelength of ∼1.2 μm with a responsivity of ∼0.17–0.38 A W −1 at −3 V. This work offers a potential pathway toward realizing tunable nanowire-based avalanche photodetectors compatible with traditional Si technology. 

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5. GaN/AIN Schottky-gate p-channel HFETs with InGaN contacts and 100 mA/mm on-current

   Bader, S.J (January 2019, IED)

   High-performance wide-bandgap p-channel devices which can be monolithically integrated with established wide-bandgap n-channel devices are broadly desirable to expand the design topologies available in power/RF electronics. This work advances the GaN-on-AIN platform as the most promising p-channel contender to enable wide-bandgap complementary electronics. Toward that end, a new generation of GaN-on-AIN-p-channel HFETs is fabricated with on-current exceeding 100mA/mm at room temperature under moderate drain bias. Key fabrication ingredients to this success are discussed, low-temperature characterizations is shared, and new results are benchmarked against the broader literature. 

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