Analysis of Schottky gate degradation evolution in AlGaN/GaN HEMTs during HTRB stress

•No electrical failure was observed on GaN HEMT under HTRB stress up to 4000h.•A gate current in excess has been observed on the Schottky diode characteristics.•This parasitic effect has been attributed to lateral surface conduction.•Formation and growing over time of pits and cracks have been observed.•These defects have been correlated with the VTh drift. GaN based technologies are promising in terms of electrical performances for power and high frequencies applications and their reliability assessment remains a burning issue. Thus, a good understanding of their degradation mechanisms is required to warranty their reliability. In this paper, an electrical parasitic effect has been observed on the gate–source diode forward characteristics of a set of devices under HTRB stress carried out at 175°C up to 4000h. This parasitic effect has been attributed to lateral surface conduction and correlated with EL signature under diode forward biasing conditions but not under transistor pinch-off biasing conditions. Then, physical analyses have pointed out the formation and growing over time of pits and cracks at the gate edge on the drain side.