Examination of Trapping Effects on Single-Event Transients in GaN HEMTs

The effect of various trapping centers on single event-transients (SETs) in GaN high-electron-mobility transistors (HEMTs) are examined via calibrated technology computer aided design (TCAD) simulations. A single-channel, Schottky-gate HEMT computational model is developed and validated with static characteristics and single-photon absorption laser data. Simulations of SETs show that a two-dimensional electron gas (2DEG) enhancement effect occurs, which leads to additional collected charge in excess of the generated charge. The origins of this effect are examined and shown to result from an increase in occupation rate of the surface donor traps as the influx of charge is developed in the charge track. Variations in trap characteristics are then introduced and their effect on internal charge collection processes examined. It is further shown the SET response is dominated by the properties of the surface donor traps (i.e., energy level and density) such that the SET drain current closely follows the transient decay of occupation rate back to the original DC level.