Time-Resolved Threshold Voltage Instability of 650-V Schottky Type p-GaN Gate HEMT Under Temperature-Dependent Forward and Reverse Gate Bias Conditions

A research on time-resolved threshold voltage instability of 650-V Schottky type p-GaN gate Al _0.2 Ga _0.8 N/GaN high electron mobility transistor (HEMT) under high-temperature gate bias (HTGB) conditions has been carried out. Both forward and reverse bias conditions are applied. We found that the threshold voltage of p-GaN AlGaN/GaN HEMT shifts negatively under high-temperature forward gate bias (HTFB), while shifts positively under high-temperature reverse gate bias (HTRB). Negative threshold voltage shifts under forward gate bias are largely due to the trapped positive charges (holes) caused by existing defects in the AlGaN layer. The holes are from the accumulated 2-D hole gas (2DHG) in the p-GaN layer near the p-GaN/AlGaN interface, which may be partially filled into the AlGaN layer by tunneling effect. Therefore, negative threshold voltage shifts under HTFB are temperature-independent. Positive threshold voltage shifts under reverse gate bias are from the hole emission in the p-GaN layer and the trapped negative charges (electrons) in the AlGaN layer. The electrons are trapped by defects resulted from the created hot holes in high temperature. The positive threshold voltage shift under HTRB is temperature-dependent, where higher temperature leads to a larger positive threshold voltage shift.