VT Shift and Recovery Mechanisms of p-GaN Gate HEMTs Under DC/AC Gate Stress Investigated by Fast Sweeping Characterization

In this work, details of stress time dependent transient V-T shift in p-GaN Gate HEMTs are captured using a fast sweeping method. A minimum saturated V-T shift (Delta V-T_Sat) independent of stress time at about 4 V gate stress is observed, and electron tunneling process assisted by shallow traps in the AIGaN barrier is introduced as a likely mechanism to explain the phenomena. Under gate stress of 6 V and above, a stress time dependent over-recovery results in a negative V-T shift before the final recovery to the fresh state, confirming that hole de-trapping process needs to take a longer time than electron de-trapping process. In addition, under AC gate stress condition, Delta V-T_Sat shows an opposite trend in cases of low and high forward AC gate bias stresses, which is explained by the difference in the trapping rates of electrons and holes.