OFF-State Drain-Voltage-Stress-Induced VTH Instability in Schottky-Type p-GaN Gate HEMTs

In this article, we systematically investigate the OFF-state drain-voltage-stress-induced threshold voltage (VTH) instability in Schottky-type p-GaN gate high electron mobility transistors (HEMTs). OFF-state drain-voltage stress and recovery tests were conducted under various temperatures and different drain biases. A sharp increase in V-TH was observed at the beginning of the stress, and V-TH kept shifting positively during the stress until it reached saturation. Further experiments showed that two different mechanisms dominated the V-TH shift, which were distinguished by the temperature dependence, degradation/recovery process and affected locations in the gate region. The hole deficiency caused by hole emission from the p-GaN layer is suggested to be the dominant reason for the V-TH instability at the beginning of the stress, while with increasing stress time, electron trapping in the barrier and buffer layers gradually dominates the V-TH shift. Based on the identified mechanisms, physics-based analytical calculations and empirical fitting are conducted to describe the V-TH behavior during the OFF-state drain-voltage stress. The fundamental mechanisms can provide a guide to develop corresponding methods to address the drain-induced V-TH instability issue.

Automated summary

This study systematically investigates the threshold voltage instability induced by OFF-state drain-voltage stress in Schottky-type p-GaN gate HEMTs. Two different mechanisms, hole deficiency and electron trapping, have been identified to dominate the shift in VTH during stress. This research provides guidance for developing methods to address the drain-induced VTH instability issue.