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The threshold voltage (V TH ) instability of a 650 V p-GaN gate AlGaN/GaN HEMTs and its underlying physical mechanism was investigated by forward gate stress. A uniquely bidirectional shift in the V TH with the critical gate voltage V critical of 6 V was observed in the device after the static and dynamic gate stress. The temperature- and time-dependent gate leakage current revealed that the occurrence of electron-trapping and hole-injection in sequence with the increasing gate bias responsible for the inhomogeneous shift in V TH . At small positive gate bias (Vg TH is induced by electron filling of acceptor-like traps in AlGaN barrier, while the gate leakage is accordingly dominated by trap-dominated SCLC. At large positive gate bias (V G >6V), the hole-injection is triggered that results in a negative shift in V TH and the gate leakage exhibits a substantial increase due to the forward turn on of the gate pn junction. Besides, the effective hole-injection also leads to a significant increase in OFF-state drain leakage, which is believed to be the pronounced electron-hole recombination in the channel.

AlGaN/GaN lateral current regulating diodes (CRDs) featuring Ohmic anodes and hybrid trench cathodes have been proposed and successfully demonstrated on silicon substrates. By the introduction of a trench with a depth of 16.4 nm in the cathode, the regulating current dramatically decreases from 457.4 to 33.1 mA/mm. In such case, the device can deliver a constant current and keep from thermal runaway under high forward bias. A maximum current hysteresis of 0.698 mA/mm is observed. The measured forward breakdown voltages of the fabricated CRDs are over 200 V in wide temperature ranges from 25 to 250 °C, and the calculated peak dynamic resistance is beyond 0.9 MΩ. Temperature dependent and pulse I-V measurements show that the CRDs possess minor temperature coefficients and fast response capabilities. Both of the two characteristics are essential for the CRD to keep a stable regulating current. Owing to the same GaN material system, the proposed CRD is potentially to be the drivers monolithically integrated with GaN-based LEDs towards a compact and robust single-chip illumination system.

In this work, a novel GaN-based reverse blocking metal-insulator-semiconductor high electron mobility transistor (RB-MISHEMT) is investigated by TCAD sentaurus. A MIS field effect drain consisting of electrically shorted Ohmic and recessed MIS structure is adopted to enable the device with high reverse blocking capability and low offset voltage. The proposed enhancement-mode (E-mode) RB-MISHEMT delivers a low reverse current of 10 μA and a low offset voltage of 0.38 V at the same time. On-state power loss of the bidirectional switch based on proposed RB-MISHEMT shows a 34% reduction compared with that of the bidirectional switch based on GaN E-mode reverse conducting MISHEMT. And the proposed E-mode RB-MISHEMT can be fabricated with standard E-mode MISHEMT technology. The high performance and fabrication compatibility of the proposed GaN RB-MISHEMT show that the device is promising for future power applications.

An efficient approach to engineering the Al2O3/GaN positive interface fixed charges (Qit+) by post-dielectric annealing in nitrogen is demonstrated. The remarkable reduction of interface fixed charges from 1.44×1013 to 3×1012 cm−2 was observed, which leads to a record high threshold voltage (VTH) of +7.6 V obtained in the Al2O3/GaN MOSFETs. The positive interface charges were proposed originating from the N-vacancy and O-substitution at the Al2O3/GaN interface and validated by Ab initio study. The device with dimensions of LG/LGS/LGD/WG = 2/1.5/5/50 µm delivers a high drain current density of 355 mA/mm. A high breakdown voltage of 1054 V @ 1 µA/mm was measured in the device with LGD of 20 µm. The results reveal that the method reported in this work is promising in pushing the VTH more positive and simultaneously achieving good device performance of normally-off GaN power devices.