Evidence for double degradation regime in off-state stressed 100 V GaN transistors: From dielectric failure to subthreshold current increase

We demonstrate the existence of two different degradation mechanisms for 100 V GaN transistors submitted to off-state stress. When the devices are stressed in strong pinch-off conditions, a high electric field falls on the dielectric between the source field plate and the channel, and a time dependent dielectric breakdown is observed. On the other hand, for weaker pinch-off, hot electrons trapping at the passivation surface can lower the electric field, leading to longer TTF. A second degradation mode is also observed, consisting in the gradual increase in off-state current, ascribed to positive charge trapping at defects spots.