Influence of the carrier behaviors in p-GaN gate on the threshold voltage instability in the normally off high electron mobility transistor

Abstract

Threshold voltage (VTH) instability has been studied in the as-fabricated p-GaN gated enhancement-mode high electron mobility transistors (p-GaN E-HEMTs) under a positive gate stress. A negative VTH shift (ΔVTH) obtained by dynamic measurement has been observed more severely when compared to the static one. The VTH deviation is attributed to the complicated influence of carrier transport behaviors in the p-GaN gate. The impacts of hole accumulation, trapping, and consumption on the VTH instability and drain current variation can be effectively distinguished according to the transfer characteristics obtained from the pulse I–V measurement. Moreover, the density of hole traps in the p-GaN gate is estimated to be around ∼2 × 1011 cm−2 by the capacitance–voltage measurement, and the energy level is calculated to be around EV + 0.62 eV by fitting the recovery curve of gate current after positive gate bias. This study focusing on the in-depth influence of different carrier behaviors on the gate performance can help with the understanding and further improvement of the dynamic instability and reliability of the GaN-based HEMTs.