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1. Robust Avalanche in 1.7 kV Vertical GaN Diodes with a Single-Implant Bevel Edge Termination

   https://doi.org/10.1109/LED.2023.3302312  

   Xiao, Ming; Wang, Yifan; Zhang, Ruizhe; Song, Qihao; Porter, Matthew; Carlson, Eric; Cheng, Kai; Ngo, Khai; Zhang, Yuhao (January 2023, IEEE Electron Device Letters)

   This work demonstrates a novel junction termination extension (JTE) with a graded charge profile for vertical GaN p-n diodes. The fabrication of this JTE obviates GaN etch and requires only a single-step implantation. A bi-layer photoresist is used to produce an ultra-small bevel angle (~0.1°) at the sidewall of a dielectric layer. This tapered dielectric layer is then used as the implantation mask to produce a graded charge profile in p-GaN. The fabricated GaN p-n diodes show a breakdown voltage ( BV ) of 1.7 kV (83% of the parallel-plane limit) with positive temperature coefficient, as well as a high avalanche current density over 1100 A/cm 2 at BV in the unclamped inductive switching test. This robust avalanche is ascribed to the migration of the major impact ionization location from the JTE edge to the main junction. This single-implant, efficient, avalanche-capable JTE can potentially become a building block of many vertical GaN devices, and its fabrication technique has wide device and material applicability. 

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2. Characterization of (001) β -Ga2O3 Schottky diodes with drift layer grown by MOCVD

   https://doi.org/10.1063/5.0155622  

   P. Sundaram, Prakash; Liu, Fengdeng; Alema, Fikadu; Osinsky, Andrei; Jalan, Bharat; Koester, Steven J. (June 2023, Applied Physics Letters)

   Growing a thick high-quality epitaxial layer on the β-Ga2O3 substrate is crucial in commercializing β-Ga2O3 devices. Metal organic chemical vapor deposition (MOCVD) is also well-established for the large-scale commercial growth of β-Ga2O3 and related heterostructures. This paper presents a systematic study of the Schottky barrier diodes fabricated on two different Si-doped homoepitaxial β-Ga2O3 thin films grown on Sn-doped (001) and (010) β-Ga2O3 substrates by MOCVD. X-ray diffraction analysis of the MOCVD-grown sample, room temperature current density–voltage data for different Schottky diodes, and C–V measurements are presented. Diode characteristics, such as ideality factor, barrier height, specific on-resistance, and breakdown voltage, are studied. Temperature dependence (170–360 K) of the ideality factor, barrier height, and Poole–Frenkel reverse leakage mechanism are also analyzed from the J–V–T characteristics of the fabricated Schottky diodes. 

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3. Robust avalanche in GaN leading to record performance in avalanche photodiode

   https://doi.org/10.1109/IRPS45951.2020.9129299  

   Ji, Dong; Ercan, Burcu; Benson, Garret; Newaz, AKM; Chowdhury, Srabanti (April 2020, 2020 IEEE International Reliability Physics Symposium (IRPS))

   This abstract presents a study on the avalanche capability of GaN p-i-n diode leading to the achievement of 60A/W, 278V GaN avalanche photodiode. The GaN p-i-n diode fabricated on a free-standing GaN substrate was avalanche capable due to optimal edge termination. Both electrical and optical characterizations were conducted to validate the occurrence of avalanche in these devices. The device showed a positive temperature coefficient of breakdown voltage, which follows the nature of avalanche breakdown. The positive coefficient was measured to be 3.85 ×10^(-4) K^(-1) (0.1V/K) under a measurement temperature ranges from 300 K to 525 K. Moreover, the fabricated device showed excellent performance as an avalanche photo detector with record device metrics: (1) record high photoresponsivity of 60 A/W; (2) high optical gain of 10^5 ; and (3) low cark current. Robust avalanche is a key requirement in various device applications and necessary for their reliable operation. 

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4. Vertical GaN Fin JFET: A Power Device with Short Circuit Robustness at Avalanche Breakdown Voltage

   https://doi.org/10.1109/IRPS48227.2022.9764569  

   Zhang, R.; Liu, J.; Li, Q.; Pidaparthi, S.; Edwards, A.; Drowley, C.; Zhang, Y. (March 2022, Vertical GaN Fin JFET: A Power Device with Short Circuit Robustness at Avalanche Breakdown Voltage)

   GaN high-electron-mobility transistors (HEMTs) are known to have no avalanche capability and insufficient short-circuit robustness. Recently, breakthrough avalanche and short-circuit capabilities have been experimentally demonstrated in a vertical GaN fin-channel junction-gate field-effect transistor (Fin-JFET), which shows a good promise for using GaN devices in automotive powertrains and electric grids. In particular, GaN Fin-JFETs demonstrated good short-circuit capability at avalanche breakdown voltage (BV AVA ), with a failure-to-open-circuit (FTO) signature. This work presents a comprehensive device physics-based study of the GaN Fin-JFET under short-circuit conditions, particularly at a bus voltage close to BV AVA . Mixed-mode electrothermal TCAD simulations were performed to understand the carrier dynamics, electric field distributions, and temperature profiles in the Fin-JFET under short-circuit and avalanche conditions. The results provide important physical references to understand the unique robustness of the vertical GaN Fin-JFET under the concurrence of short-circuit and avalanche as well as its desirable FTO signature. 

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5. Schottky contacts to N-polar GaN with SiN interlayer for elevated temperature operation

   https://doi.org/10.1063/5.0083588  

   Khachariya, Dolar; Szymanski, Dennis; Reddy, Pramod; Kohn, Erhard; Sitar, Zlatko; Collazo, Ramón; Pavlidis, Spyridon (April 2022, Applied Physics Letters)

   In this Letter, we unveil the high-temperature limits of N-polar GaN Schottky contacts enhanced by a low-pressure chemical vapor deposited (LPCVD) SiN interlayer. Compared to conventional Schottky diodes, the insertion of a 5 nm SiN lossy dielectric interlayer in-between Ni and N-polar GaN increases the turn-on voltage ( V ON ) from 0.4 to 0.9 V and the barrier height ( ϕ B ) from 0.4 to 0.8 eV. This modification also reduces the leakage current at zero bias significantly: at room temperature, the leakage current in the conventional Schottky diode is >10 3 larger than that observed in the device with the SiN interlayer, while at 200 °C, this ratio increases to 10 5 . Thus, the rectification ratio (I ON /I OFF ) at ±1.5 V reduces to less than one at 250 °C for the conventional Schottky diode, whereas for SiN-coated diodes, rectification continues until 500 °C. The I–V characteristics of the diode with an SiN interlayer can be recovered after exposure to 400 °C or lower. Contact degradation occurs at 500 °C, although devices are not destroyed yet. Here, we report N-polar GaN Schottky contact operation up to 500 °C using an LPCVD SiN interlayer. 

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