Analytical model of the frequency-dependent output conductance of GaAs, MESFETs on semi-insulating substrates

We propose an analytical model for the frequency-dependent output conductance of GaAs MESFETs on semi-insulating (SI) substrates. Because of deep levels the ac potential profile across the SI region between source and drain is frequency dependent and results in a change with frequency of the ac voltage drop across the channel-substrate interface. This results in a change of the output conductance with frequency. A closed form for the ac potential profile was obtained by solving the continuity equations for holes and electrons plus Poissson's equation under conditions of low-level injection and low frequencies. The model allows an examination of the effect of the density and location of multiple deep levels and reproduces published experimental and numerical results.