AVALANCHE BREAKDOWN AND SURFACE DEEP-LEVEL TRAP EFFECTS IN GAAS-MESFETS

Time-dependent numerical simulations have been performed to investigate avalanche breakdown and surface deep-level trapping effects in GaAs MESFET's. The model is based on a combination of bipolar drift-diffusion transport, impact ionization, and a dynamic surface charging mechanism. A realistic trapping process is introduced into the surface trap model from which the spatial distribution of surface charge density is determined. The basic breakdown mechanisms, gate-bias-dependent breakdown voltages, and effects of surface charges are demonstrated. It is shown that the surface deep-level traps have a pronounced effect on the breakdown phenomenon.