Two dimensional numerical modeling and simulation of a uniformly doped GaAs MESFET photodetector

This paper presents a two dimensional numerical model for determining the d.c. characteristics of uniformly doped GaAs-MESFET (Metal semiconductor field effect transistor). The model takes into account all the major effects that determine the device characteristics in the illuminated condition, The 2-D potential distribution function in the active layer of the device is approximated as a parabolic function and the 2-D Poisson's equation has been solved with suitable boundary conditions to obtain the surface potential. The calculations have been carried out for uniform doping profile in two dimensions. Calculations have been carried out numerically for a GaAs-MESFET to examine the effect of illumination on current-voltage characteristics, depletion capacitance (Cdp), internal gateto-source capacitance (C gs), drain-to-source resistance (Rds) and transconductance (gm). The model takes into account the effect of photo-generation in the semi -insulating substrate region. The estimation of the channel voltage profile and the drain current characteristics has been obtained for the calculation of photo induced voltages at the Schottky contact under illumination. The model can be used to obtain the drain and the transfer characteristics under dark and illuminated conditions. The results show that the performance of the device is good and it can be used as photodetector for OEICs (Opto Electronic Integrated Circuits) applications. The proposed model is simple and easy to understand the behavior of the uniformly doped MESFET as compared to the other models reported in the literature.