Schottky Gate Induced Threshold Voltage Instabilities in p-GaN Gate AlGaN/GaN HEMTs

We present detailed ON-state gate current characterization of Schottky gate p-GaN capped AlGaN/GaN high-electron-mobility transistors (HEMTs) on two distinct gate processes. The threshold voltage is monitored from $10~mathrm {mu } ext{s}$ up to 100 s under positive gate bias stress and during recovery. The threshold voltage stability is affected by the balance between hole and electron current in the gate stack. More specifically, devices with uniform hole conduction across the p-GaN gate area demonstrate stable threshold voltage behavior up to $V_{g}=5,mathrm {V}$ , whereas devices with a dominating gate perimeter electron conduction demonstrate larger instabilities. Finally, the threshold voltage stability during OFF-state pulsed stress is investigated and correlated to the excess gate-to-drain charge extracted from capacitance curves.