Experimental evaluation of interface states during time-dependent dielectric breakdown of GaN-based MIS-HEMTs with LPCVD-SiNx gate dielectric*

We experimentally evaluated the interface state density of GaN MIS-HEMTs during time-dependent dielectric breakdown (TDDB). Under a high forward gate bias stress, newly increased traps generate both at the SiN x /AlGaN interface and the SiN x bulk, resulting in the voltage shift and the increase of the voltage hysteresis. When prolonging the stress duration, the defects density generated in the SiN x dielectric becomes dominating, which drastically increases the gate leakage current and causes the catastrophic failure. After recovery by UV light illumination, the negative shift in threshold voltage (compared with the fresh one) confirms the accumulation of positive charge at the SiN x /AlGaN interface and/or in SiN x bulk, which is possibly ascribed to the broken bonds after long-term stress. These results experimentally confirm the role of defects in the TDDB of GaN-based MIS-HEMTs.