Analysis of lags and current collapse in source-field-plate AlGaN/GaN high-electron-mobility transistors

A two-dimensional transient analysis of source-field-plate AlGaN/GaN high-electron-mobility transistors (HEMTs) is performed by considering a deep donor and a deep acceptor in a buffer layer, and the results are compared with those in the case of gate-field-plate structures. It is shown that the reduction rate of drain lag obtained by introducing a field plate is quantitatively similar between source- and gate-field-plate structures. However, the gate-lag rate is rather higher in the source-field-plate structure because the electric field at the drain edge of the gate is higher in the off state, and hence electron injection into the buffer layer and the resulting trapping effects are more significant. Hence, current collapse is slightly larger in the source-field-plate structure. It is also shown that an optimum SiN passivation layer thickness is required to minimize buffer-related current collapse in source-field-plate AlGaN/GaN HEMTs.