ON-State Gate Stress Induced Threshold Voltage Instabilities in p-GaN Gate AlGaN/GaN HEMTs

In this study, the transient threshold voltage behavior of p-GaN capped AlGaN/GaN high-electron-mobility transistors (HEMTs) is evaluated, by monitoring the threshold voltage from 10 mu s up to 100 s during positive gate bias stress, as well as during recovery. It is found that the threshold voltage transients are highly dependent on the current distribution in the metal/p-GaN/AlGaN/GaN gate stack. Two different gate processes are evaluated in terms of os-state gate current, gate conduction mechanism and threshold voltage stability. Devices with perimeter-dependent gate current show large threshold voltage shifts; devices in which the gate current is due to uniform thermionic (field) emission over the Schottky interface into the bulk p-GaN demonstrate stable behavior for V-g < 5 V.