Recovery mechanism of reverse leakage current in GaN HEMTs following thermal storage test

High leakage current in reverse bias is a widely reported reliability issue in AlGaN/GaN high electron mobility transistors (HEMTs). The material quality and the electric field at the gate terminal accounts for various tunnelling processes contributing to the observed leakage currents. In this study, the HEMTs were subjected to 573K (300^OC) for 8 and 12 hrs and the reverse gate leakage current was observed at V_GS = -8V and V_DS = 5V throughout a period of 72 hrs. The gate current was modelled using phonon assisted tunnelling (PAT) and trap assisted tunnelling (TAT) components for a range of temperatures as well as after 72 hrs recovery from 573K. The extracted density of interface states (D_it) values (0.4 – 4.9 x 10¹⁴ cm^-2) follow a monotonic trend with increasing temperatures showing increased PAT dominated current above a critical temperature (T > 500K). The presence of deep AlGaN barrier trap (1.18 eV) activates the TAT component as well as slows down the recovery through slow emission from the trap centres. This is experimentally found from the characteristic recovery time period around 5 - 13 hrs. The post recovery current values are observed to be one order higher than the pristine values suggesting a partial degradation in the devices due to the applied thermal stress.