Study of AlGaN/GaN HEMT degradation through TCAD simulations

This paper studies, through Three-Dimensional (3D) TCAD simulations, the formation of gate edge pits on the drain-side of GaN high electron mobility transistors (HEMTs) under electrical stress conditions. These pits are believed to be formed due to electrochemical reactions. The simulations predict that holes, which are necessary to initiate the electrochemical reaction but rare under regular HEMT operating conditions, can be generated through trap-assisted, band-to-band tunneling (B2B TAT). The impact of the electrical behavior of the pit (insulator or metal) on the output characteristics (I_D-V_D) of the HEMTs were also studied. Insulator-type pits degrade the ON-resistance, R_D, while metal-types do not. At medium V_D, both types of pit degrade I_D, which will be recovered at higher V_D. But metal-type requires larger V_D to restore the I_D. As the pits grow, the hole generation rate first increases (more with metal pit), then decrease after the pit-to-width ratio exceeds 20%.