Simulation and verification of vertical gallium nitride power diodes

Abstract

Gallium nitride (GaN), a direct, wide bandgap semiconductor, has been the subject of a rapidly growing field of study in power semiconductor research, as its large bandgap results in a high critical electric field and temperature resilience that is desired in high voltage, high current applications. Recent improvements in the quality of bulk GaN substrates have made vertical GaN devices feasible, and the large active areas and drift region lengths of vertical devices allow for lower on-resistance and high breakdown voltage. Due to the incipient nature of this field, the volume of experimental data is sparse, and thus there is a need for accurate simulation models to allow for device design and optimization. In this work, a model for GaN is presented, developed using the results of the most recent experimental and Monte-Carlo simulation data. This model is then verified for experimentally tested vertical GaN Schottky barrier diodes and p-n diodes with simple device geometry in both forward and reverse bias breakdown conditions. To take full advantage of the high critical field and maximize breakdown voltage, electric-field crowding at the device edges must be minimized, so various edge-termination structures are simulated, from which significant improvement to breakdown is observed.