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1. Distributed polarization-doped GaN p–n diodes with near-unity ideality factor and avalanche breakdown voltage of 1.25 kV

   https://doi.org/10.1063/5.0083302  

   Nomoto, Kazuki ; Li, Wenshen ; Song, Bo ; Hu, Zongyang ; Zhu, Mingda ; Qi, Meng ; Protasenko, Vladimir ; Zhang, Zexuan ; Pan, Ming ; Gao, Xiang ; et al ( March 2022 , Applied Physics Letters)

   Polarization-induced (Pi) distributed or bulk doping in GaN, with a zero dopant ionization energy, can reduce temperature or frequency dispersions in impurity-doped p–n junctions caused by the deep-acceptor-nature of Mg, thus offering GaN power devices promising prospects. Before comprehensively assessing the benefits of Pi-doping, ideal junction behaviors and high-voltage capabilities should be confirmed. In this work, we demonstrate near-ideal forward and reverse I–V characteristics in Pi-doped GaN power p–n diodes, which incorporates linearly graded, coherently strained AlGaN layers. Hall measurements show a net increase in the hole concentration of 8.9 × 10¹⁶ cm⁻³in the p-layer as a result of the polarization charge. In the Pi-doped n-layer, a record-low electron concentration of 2.5 × 10¹⁶ cm⁻³is realized due to the gradual grading of Al_0-0.72GaN over 1  μm. The Pi-doped p–n diodes have an ideality factor as low as 1.1 and a 0.10 V higher turn-on voltage than the impurity-doped p–n diodes due to the increase in the bandgap at the junction edge. A differential specific on-resistance of 0.1 mΩ cm²is extracted from the Pi-doped p–n diodes, similar with the impurity-doped counterpart. The Pi-doped diodes show an avalanche breakdown voltage of ∼1.25 kV, indicating a high reverse blocking capability even without an ideal edge-termination. This work confirms that distributed Pi-doping can bemore »incorporated in high-voltage GaN power devices to increase hole concentrations while maintaining excellent junction properties.

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2. Breakdown characteristics of deep-ultraviolet Al _0.6 Ga _0.4 N p-i-n avalanche photodiodes

   https://doi.org/10.1063/5.0073515  

   Jeong, Hoon ; Cho, Minkyu ; Xu, Zhiyu ; Mehnke, Frank ; Bakhtiary-Noodeh, Marzieh ; Detchprohm, Theeradetch ; Shen, Shyh-Chiang ; Otte, Nepomuk ; Dupuis, Russell D. ( March 2022 , Journal of Applied Physics)

   A top-illuminated deep-ultraviolet Al_0.6Ga_0.4N p-i-n avalanche photodiode (APD) structure was designed and grown by metalorganic chemical vapor deposition on an AlN bulk substrate and on two different quality AlN/sapphire templates, and APDs were fabricated and tested. The APD devices with a circular diameter of 20  μm have demonstrated a distinctive reverse-bias breakdown behavior. The reverse breakdown voltage of the APDs is approximately −140 V, which corresponds to a breakdown electric field of 6–6.2 MV/cm for the Al_0.6Ga_0.4N material as estimated by Silvaco TCAD simulation. The APDs grown on the AlN bulk substrate show the lowest leakage current density of <1 × 10⁻⁸ A/cm²(at low reverse bias) compared to that of the devices grown on the AlN templates. From the photocurrent measurement, a maximum gain (current limited) of 1.2 × 10⁴is calculated. The average temperature coefficients of the breakdown voltage are negative for APD devices fabricated from both the AlN bulk substrate and the AlN templates, but these data show that the coefficient is the least negative for the APD devices grown on the low-dislocation-density AlN bulk substrate.
3. 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.
4. 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.
5. Exceptional Repetitive-Short-Circuit Robustness of Vertical GaN Fin-JFET at High Voltage

   https://doi.org/10.1109/ISPSD49238.2022.9813618  

   Zhang, R. ; Liu, J. ; Li, Q. ; Pidaparthi, S. ; Edwards, A. ; Drowley, C. ; Zhang, Y. ( May 2022 , Exceptional Repetitive-Short-Circuit Robustness of Vertical GaN Fin-JFET at High Voltage)

   The limited short circuit (SC) capability of GaN high-electron-mobility transistors (HEMTs) has become a critical concern for their adoption in many power applications. Recently, breakthrough SC robustness was demonstrated in a 650-V rated vertical GaN Fin-JFET with a short circuit withstanding time of over 30 µs at 400 V bus voltage (V BUS ), showing great potential for automotive powertrain and grid applications. This work presents the first study on the repetitive SC robustness of this GaN Fin-JFET at a V BUS of 400 V and 600 V. The GaN Fin-JFET survived 30,000 cycles of 400 V, 10 µs SC stresses without any degradation in device characteristics. At a 600 V V BUS , it survived over 8,000 cycles of 10 µs SC stresses before an open-circuit failure. This open-circuit failure signature allows the GaN Fin-JFET to retain its avalanche breakdown voltage and is highly desirable for system safety. Besides, an increase in gate leakage was observed during the 600 V repetitive test, which can be used as a precursor to predict device failure. As far as we know, this is the first report of an exceptional repetitive SC robustness in a power transistor at a V BUS close tomore »its rated voltage.« less