Frequency- and Temperature-Dependent Gate Reliability of Schottky-Type p-GaN Gate HEMTs

In this paper, we carried out a systematic investigation on gate degradation and the physical mechanism of the Schottky-type p-GaN gate HEMTs under positive gate voltage stress. The frequency-and temperature-dependent measurements have been conducted. It is found that the time-dependent gate degradation exhibits weak relevance with frequencies ranging from 10 to 100 kHz under dynamic gate stress and is similar to that in static gate stress. Both the gate breakdown voltage (BV) and mean-time-to-failure (MTTF) show positive temperature dependence. Moreover, the current-voltage (I-V) characteristics and threshold voltage (V-TH) instability of p-GaN devices before/after gate degradation are compared and analyzed. The degraded Schottky junction exhibits an ohmic-like gate behavior. It is revealed that under a large gate bias stress, high-energy electrons accelerated in the depletion region of the p-GaN layer would promote the formation of defect levels near the metal/p-GaN interface, leading to the initial p-GaN layer degradation. The subsequent high gate leakage density could cause the final degradation of the AlGaN barrier.