Analysis of buffer-trapping effects on gate lag, drain lag and current collapse in AlGaN/GaN HEMTs

Transient simulations of AlGaN/GaN HEMTs are performed in which a deep donor and a deep acceptor are considered in a semi-insulating buffer layer. Quasi-pulsed I-V curves are derived from the transient characteristics, and are compared with steady-state I-V curves. It is shown that the lag phenomena and current collapse could be reproduced. Particularly, the gate lag is correlated with relatively high source access resistance of the FETs. The current collapse is shown to bemore 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 collapse in AlGaN/GaN HEMTs, an acceptor density in the buffer layer should be made low, although the current cutoff behavior may be degraded.