Bidirectional threshold voltage shift and gate leakage in 650 V p-GaN AlGaN/GaN HEMTs: The role of electron-trapping and hole-injection

Abstract

The threshold voltage (VTH) 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 VTH with the critical gate voltage Vcritical 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 VTH. At small positive gate bias (Vg<6V), the positive shift in VTH 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 (VG>6V), the hole-injection is triggered that results in a negative shift in VTH 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.