We make a two-dimensional transient analysis of field-plate AlGaN/GaN high electron mobility transistors (HEMTs) with a Fe-doped semi-insulating buffer layer, which is modeled that as deep levels, only a deep acceptor located above the midgap is included (EC − EDA = 0.5 eV, EC: energy level at the bottom of conduction band, EDA: deep acceptor's energy level). And the results are compared with a case having an undoped semi-insulating buffer layer in which a deep donor above the midgap (EC − EDD = 0.5 eV. EDD: the deep donor's energy level) is considered to compensate a deep acceptor below the midgap (EDA − EV = 0.6 eV, EV: energy level at the top of valence band). It is shown that the drain-current responses when the drain voltage is lowered abruptly are reproduced quite similarly between the two cases with different types of buffer layers, although the time region where the slow current transients occur is a little different. The lags and current collapse are reduced by introducing a field plate. This reduction in lags and current collapse occurs because the deep acceptor's electron trapping is reduced under the gate region in the buffer layer. The dependence of drain lag, gate lag and current collapse on the field-plate length and the SiN layer thickness is also studied, indicating that the rates of drain lag, gate lag and current collapse are quantitatively quite similar between the two cases with different types of buffer layers when the deep-acceptor densities are the same.
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