Degradation and Failure Mechanism of p-GaN Gate E-Mode GaN HEMTs

Abstract

This work describes the cause-effect-based degradation process of the p-GaN gate in Enhancement-mode (E-mode) GaN High Electron Mobility Transistors (HEMTs) using gate stressing and failure analysis (FA). We found no correlation between time-to-fail and initial gate current (IG0). Instead, a higher impact of temperature was found on the gate current of the device (IG) and time-to-fail at 100 °C. Gate failure at constant voltage stress was a single-stage failure. Under constant current stress, the gate shows a multi-stage failure. The breakdown starts with increased gate current leading to Schottky barrier leakage and finally to catastrophic contact failure. The metal/p-GaN interface at the gate finger becomes the weakest part of the gate stack. Metal/p-GaN interface and surface defects develop as percolation paths acting as leakage sources, and nano-cracks have been observed in the gate cap. FA also shows physical degradation at the metal/p-GaN cap due to electrical stress.