Simulation of current slump removal in field-plate GaAs MESFETs with a thin passivation layer

Two-dimensional transient analysis of field-plate GaAs MESFETs is performed by considering surface states in the region from the gate toward the drain. The field-plate length L_FP and the thickness of SiO₂ passivation layer T_i are varied as parameters. It is shown that the drain lag is not removed when T_i is thick even if L_FP is longer than the length of surface-state region L_s. But when T_i becomes thinner than 0.02 μm, the drain lag, gate lag and current slump are completely removed by introducing a field plate longer than L_s because the surface-state effects may be masked. By carefully examining the L_FP dependence of lags and current collapse for T_i = 0.02 μm, they are found to be completely removed even if L_FP is alittle shorter than L_s.