Influence of field dependent mobility and buffer isolation resistance on high frequency performances of GaAs MESFET´s

The aim of this paper is to present an analytical model which describes the dynamical properties of GaAs MESFET. First the admittance matrix of the active unsaturated region is derived from a new wave equation which includes the mobility dependence on the electric field. Second the admittance matrix of the whole device is calculated. Leakage effects across the buffer layer are considered. It turns out that variations of the admittance and scattering parameters as well as the power gain variations with drain current are accurately predicted. The gain peaks at a drain current value close to IDSSwhich is attributed to the combined influence of field dependent mobility and parasitic stray. It is pointed out that devices with perfectly insulating buffer can exhibit a microwave power gain which is 5 dB higher than in real devices.