Numerical simulation of drain-current transients and current compression in GaN MESFETs

Transient simulations of GaN MESFETs are performed in which a three-level, compensation model is adopted for a semi-insulating buffer layer, where a shallow donor, a deep donor and a deep acceptor are considered. Quasi-pulsed I-V curves are derived from the transient characteristics, and are compared with steady-state I-V curves. It is shown that so-called current compression is more pronounced when the deep-acceptor density in the buffer layer is higher and when an off-state drain voltage is higher, because trapping effects become more significant. It is suggested that to minimize current compression in GaN-based FETs, an acceptor density in a semi-insulating GaN layer should be made low.