The Dependence of off-State Breakdown of AlGaN/GaN HEMTs on Buffer Traps, Gate Bias and Field Plate

Abstract

We investigate AlGaN/GaN HEMTs which show a large increase in measured off-state breakdown voltage, V_BR, from near-V_T to deep-off state V_GS conditions, accompanied by a positive shift in measured V_T, when these devices are stressed electrically by alternating I_D–V_GS and I_D–V_DS measurements. We show that, if stress is assumed to cause spatially uniform changes, the above variations in V_BR and V_T can be explained in terms of increased ionized deep acceptor trap concentration in the GaN buffer. We also show that, the near-V_T V_BR is due to space-charge limited current while the deep off-state V_BR is due to impact ionization. Our simulations predict that the incorporation of a field plate in the device can enhance the latter V_BR significantly, but may not change the former V_BR much.