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 (ID-VD) of the HEMTs were also studied. Insulator-type pits degrade the ON-resistance, RD, while metal-types do not. At medium VD, both types of pit degrade ID, which will be recovered at higher VD. But metal-type requires larger VD to restore the ID. As the pits grow, the hole generation rate first increases (more with metal pit), then decrease after the pit-to-width ratio exceeds 20%.