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.

This work examines a new hybrid edge termination structure for vertical GaN diodes. The hybrid JTE-GR termination consists of superimposed guard rings (GRs) onto a junction termination extension (JTE), resulting in zones with alternating implantation depths. The charge profile of the hybrid termination is developed by integrating the charge in the termination region across its length. An optimization strategy for designing the geometry is proposed by fitting the charge profile in the termination to that of a negative bevel edge reference termination. As the number of rings ranges from 4 to 12, it is shown via simulation that the optimized hybrid structure exhibits breakdown voltages between 92% and 95% of the ideal parallel plane breakdown voltage. Despite having similar breakdown voltages, by increasing the number of rings, the charge profile of the reference bevel termination is more closely fit. This results in a better approximation of the breakdown voltage response to variations in the p-layer doping concentration and thickness. The proposed design methodology and structure allow the design of high-voltage device termination geometry with minimal computationally expensive TCAD optimization.