Analysis of buffer-related lag phenomena and current collapse in GaN FETs

Drain-current responses of GaN MESFETs with a semi-insulating buffer layer are calculated when the drain voltage and/or the gate voltage are changed abruptly, and pulsed I-V curves are derived from them. It is shown that so-called current collapse or current slump is not so dependent on the gate length L_G (0.3 μm - 1 μm), and this is essentially determined by a deep-acceptor density N_DA in the buffer layer. L_G and N_DA dependence of gate lag is also studied, indicating that the gate lag is weaker for longer L_G and the lag rate becomes high with N_DA, although it may show a saturation behaviour.