Numerical analysis of pulsed I-V curves and current collapse in GaN FETs as affected by buffer trapping

Abstract

Two-dimensional transient analysis of GaN MESFETs is 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 the steady-state I-V curves. It is shown that so-called current collapse or current reduction is more pronounced when the deep-acceptor density in the buffer layer is higher and when an off-state drain voltage is higher, because the trapping effects become more significant. It is suggested that to minimize current collapse in GaN-based FETs, an acceptor density in a semi-insulating GaN layer should be made low, although the current cutoff behaviour may be degraded.