Computational analysis of breakdown voltage enhancement for AlGaN/GaN HEMTs through optimal pairing of deep level impurity density and contact design

Abstract

Simulations are used to explore the possibility of achieving breakdown voltage scaling using deep acceptors in the buffer for AlGaN/GaN HEMTs. The existence of an optimal range of deep level acceptor density (1017cm−3), for which the electric field shows the most uniform distribution over the entire Lgd is demonstrated. The peak electric field can be capped off at a certain value, which can be engineered using deep level defects to be less than the critical electric field for GaN or the critical field for punch-through, whichever is lower. Following the saturation in peak electric field, the additional applied voltage spreads across the device access region. Thus, precise control of defect incorporation in the GaN buffer is shown to be a key factor in achieving high breakdown voltage HEMTs with improved unipolar figure of merit. A novel scheme for the source and drain contacts, using shallow mesa etch and partial mesa sidewall oxidation to increase the allowed range of variation in optimal acceptor density to achieve uniform electric field distribution is presented.