Charge feedback mechanisms at forward threshold voltage stress in GaN/AlGaN HEMTs

Charge trapping in the insulating layer of gallium-nitride (GaN) metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) is a serious reliability challenge but is still poorly understood. We demonstrate here that the observed Vth drift and recovery can be understood as charge capture and emission following a non-radiative multi-phonon (NMP) mechanism into traps with widely distributed properties. Furthermore, due to the large amount of trapped charge, the feedback of that charge on the surface potential and thus on the capture and emission times has to be considered self-consistently in order to correctly explain the temporal changes in their distributions.