On the physics link between time-dependent gate breakdown and electroluminescence in Schottky-type p-GaN gate HEMTs

In this paper, Schottky-type p-GaN gate HEMTs with semi-transparent gate electrodes were fabricated. The time-dependent forward gate breakdown (TDB) was investigated and a two-stage degradation process was identified and analyzed. The first degradation induced gate current increase and the second degradation caused complete gate failure, respectively. 78 of 100 devices under test followed this two-stage degradation process. Combining with the time-dependent electroluminescence (TDEL) characteristics, the Schottky-metal/p-GaN (M-S) junction was demonstrated to be the vulnerable part under the long-term positive gate stress, leading to the first degradation. Afterward, the hole blocking capability vanished and significant hole injection happened through the M-S junction. This not only enhanced the EL emission intensity but also enlarged the electric field across the p-GaN/AlGaN/GaN (P-i-N) junction. Finally, the second degradation happened on the P-i-N junction and resulted in the complete gate breakdown.