Observation of self-recoverable gate degradation in p-GaN AlGaN/GaN HEMTs after long-term forward gate stress: The trapping & detrapping dynamics of hole/electron

The gate reliability of normally off p-GaN gate AlGaN/GaN HEMTs and its underlying physical mechanism were investigated in a long-term recovery period after long-term forward gate stress. For the first time, a nondestructive gate degradation featuring a first degradation and then followed by a self-recovery dynamic was observed after a rigorous long-term (13-53 ks) forward gate stress. To elucidate the gate degradation kinetics, the static gate current, transfer characteristic and transient gate current were characterized before and after the gate stress as well as in the recovery intervals. During the stress, hole-injection together with trap-generation and hole-trapping concurred in AlGaN barrier is observed. Subsequently, electrons attracted by the trapped holes are persistently trapped in the AlGaN barrier, which leads to an electron energy barrier lowering and a continuing gate current increase in the recovery intervals. The hole-injection, hole-trapping, electron-trapping and hole/electron-detrapping take place in sequence during the stress and recovery process are reinforced by the inhomogeneous shift in VTH. The observed unique gate degradation dynamics and its underlying mechanism are of great value for p-GaN gate optimization to achieve improved gate reliability.