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1. First Demonstration of Vertical Superjunction Diode in GaN

   https://doi.org/10.1109/IEDM45625.2022.10019405  

   Xiao, Ming; Ma, Yunwei; Du, Zhonghao; Qin, Yuan; Liu, Kai; Cheng, Kai; Udrea, Florin; Xie, Andy; Beam, Edward; Wang, Boyan; et al (December 2022, First Demonstration of Vertical Superjunction Diode in GaN)

   We report the first experimental demonstration of a vertical superjunction device in GaN. P-type nickel oxide (NiO) is sputtered conformally in 6μm deep n-GaN trenches. Sputter recipe is tuned to enable 1017 cm −3 level acceptor concentration in NiO, easing its charge balance with the 9×1016 cm −3 doped n-GaN. Vertical GaN superjunction p-n diodes (SJ-PNDs) are fabricated on both native GaN and low-cost sapphire substrates. GaN SJ-PNDs on GaN and sapphire both show a breakdown voltage (BV) of 1100 V, being at least 900 V higher than their 1-D PND counterparts. The differential specific on-resistance (RON,SP) of the two SJ-PNDs are both 0.3mΩ⋅ cm 2 , with the drift region resistance (RDR,SP) extracted to be 0.15mΩ⋅ cm 2 . The RON,SP∼BV trade-off is among the best in GaN-on-GaN diodes and sets a new record for vertical GaN devices on foreign substrates. The RDR,SP∼BV trade-off exceeds the 1-D GaN limit, fulfilling the superjunction functionality in GaN. 

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2. Properties and device performance of BN thin films grown on GaN by pulsed laser deposition

   https://doi.org/10.1063/5.0092356  

   Biswas, Abhijit; Xu, Mingfei; Fu, Kai; Zhou, Jingan; Xu, Rui; Puthirath, Anand B.; Hachtel, Jordan A.; Li, Chenxi; Iyengar, Sathvik Ajay; Kannan, Harikishan; et al (September 2022, Applied Physics Letters)

   Wide and ultrawide-bandgap semiconductors lie at the heart of next-generation high-power, high-frequency electronics. Here, we report the growth of ultrawide-bandgap boron nitride (BN) thin films on wide-bandgap gallium nitride (GaN) by pulsed laser deposition. Comprehensive spectroscopic (core level and valence band x-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and Raman) and microscopic (atomic force microscopy and scanning transmission electron microscopy) characterizations confirm the growth of BN thin films on GaN. Optically, we observed that the BN/GaN heterostructure is second-harmonic generation active. Moreover, we fabricated the BN/GaN heterostructure-based Schottky diode that demonstrates rectifying characteristics, lower turn-on voltage, and an improved breakdown capability (∼234 V) as compared to GaN (∼168 V), owing to the higher breakdown electrical field of BN. Our approach is an early step toward bridging the gap between wide and ultrawide-bandgap materials for potential optoelectronics as well as next-generation high-power electronics. 

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3. 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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4. TCAD Simulation Models, Parameters, and Methodologies for β-Ga ₂ O ₃ Power Devices

   https://doi.org/10.1149/2162-8777/accfbe  

   Wong, Hiu Yung (May 2023, ECS Journal of Solid State Science and Technology)

   β-Ga₂O₃is an emerging material and has the potential to revolutionize power electronics due to its ultra-wide-bandgap (UWBG) and lower native substrate cost compared to Silicon Carbide and Gallium Nitride. Sinceβ-Ga₂O₃technology is still not mature, experimental study ofβ-Ga₂O₃is difficult and expensive. Technology-Computer-Aided Design (TCAD) is thus a cost-effective way to study the potentials and limitations ofβ-Ga₂O₃devices. In this paper, TCAD parameters calibrated to experiments are presented. They are used to perform the simulations in heterojunction p-NiO/n-Ga₂O₃diode, Schottky diode, and normally-off Ga₂O₃vertical FinFET. Besides the current-voltage (I-V) simulations, breakdown, capacitance-voltage (C-V), and short-circuit ruggedness simulations with robust setups are discussed. TCAD Sentaurus is used in the simulations but the methodologies can be applied in other simulators easily. This paves the road to performing a holistic study ofβ-Ga₂O₃devices using TCAD. 

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5. Vertical GaN junction barrier Schottky diodes with near-ideal performance using Mg implantation activated by ultra-high-pressure annealing

   https://doi.org/10.35848/1882-0786/ac8f81  

   Khachariya, Dolar; Stein, Shane; Mecouch, Will; Breckenridge, M. Hayden; Rathkanthiwar, Shashwat; Mita, Seiji; Moody, Baxter; Reddy, Pramod; Tweedie, James; Kirste, Ronny; et al (September 2022, Applied Physics Express)

   Abstract We report a kV class, low ON-resistance, vertical GaN junction barrier Schottky (JBS) diode with selective-area p-regions formed via Mg implantation followed by high-temperature, ultra-high pressure (UHP) post-implantation activation anneal. The JBS has an ideality factor of 1.03, a turn-on voltage of 0.75 V, and a specific differential ON-resistance of 0.6 mΩ·cm 2 . The breakdown voltage of the JBS diode is 915 V, corresponding to a maximum electric field of 3.3 MV cm −1 . These results underline that high-performance GaN JBS can be realized using Mg implantation and high-temperature UHP post-activation anneal. 

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