Investigation of Electrical Breakdown in AlGaN/GaN/AlN HEMTs Through Nanoscale Analysis and Physics-Based Modeling

The high-voltage operation of GaN power high-electron mobility transistors (HEMTs) is primarily limited by electric field crowding near the gate field plates, which, over time, can degrade the dielectric properties of the passivation layer or gate insulators and compromise device reliability. Therefore, understanding the different breakdown mecha-nisms—X;their causes and locations—X;is essential for optimizing device design and improving off-state performance. Previous studies have primarily focused on device reliability in GaN HEMTs with doped buffer layers. By contrast, this study fo-cuses on the effects of prolonged off-state stress in Metal-Insu-lator-Semiconductor (MIS)-gated GaN HEMT with an Al-GaN/GaN/AlN heterostructure design without a buffer layer. The devices are investigated using electrical characteriza-tion, nanoscale structural/chemical analysis (SEM, TEM, EDS). Additionally, technology computer-aided design (TCAD) simulations are employed to describe the breakdown process by studying the electric field and charge distribution in the dielectrics. Based on the structural/chemical analysis, as well as the TCAD simulation results, it is suggested that the formation of a vertical percolation path in the SiNx passivation layer underneath the field plate edge initiates the destructive breakdown process.