Model for dc and rf characteristics of optically biased GaN metal semiconductor field effect transistor for electronic/optoelectronic microwave applications

An analytical model to analyze the effect of light on the dc and rf characteristics of a GaN metal semiconductor field effect transistor (MESFET) is presented. The photovoltaic effect in the depletion region and gate length modulation in the active channel is considered using an unidimensional approach. The parasitic resistances are made illumination dependent by considering the photovoltage developed across the Schottky barrier, causing gate-voltage modulation in the ungated portions of the channel. Also, the sidewall capacitance is evaluated, taking into account the illumination-modulated fringing charge. These effects are then used to predict the cut-off frequency, admittance parameters, and scattering parameters of the device.