The paper deals with 2D numerical modeling of Si-SiO<sub>2</sub> MOSFET for considering the field dependent mobility of the carriers in the surface channel. The fundamental device equations have been numerically solved to obtain various characteristics and parameters. The surface potential and electric field profile in the channel have been numerically estimated to have indepth analysis. The model enables one to estimate various parameters which determine the potential use of this device for various applications. The noise analysis of the device has been carried out to study the performance of the device. The exact solution of the 2D Poisson's equation for the S<sub>i</sub>-S<sub>i</sub>O<sub>2</sub> MOSFET's is derived by using Liebmann's iteration method. Based on the derived 2D potential distribution, the surface potential distribution in the S<sub>i</sub> film is numerically obtained and their accuracy is verified by 2D analytical analysis. The calculated minimum surface potential and its location are used to analyze the drain-induced barrier-lowering effect and further to develop numerical threshold - voltage model. It is shown that excellent agreements are obtained for wide ranges of device structure parameters and applied biases.
A two-dimensional numerical model of GaAs MESFET with non uniform doping is developed and various characteristics are estimated under different illumination conditions. The Poisson's equations in the gate depletion region and the space charge region of the channel substrate junctions are solved numerically under dark and illumination condition. The photo induced voltages at the schottky contact (V<sub>op</sub>) as well as at the junction between channel and substrate (V<sub>ops</sub>) are calculated for estimating the channel voltage profile and the drain current characteristics. It has been seen that the depletion widths are strongly influenced by illumination and hence the characteristics. The model developed here can be used to obtain the drain and the transfer characteristics cunder dark and illuminated conditions. The device parameters such as transconductance and gate to source capacitance are numerically estimated to examine the switching characteristics of the device. The photo current has also been estimated and the responsivity of the device has been calculated. The responsivity is found to be very high. The switching speed has also increased under illumination because of the decrease in the RC time constant. It has been concluded that the two dimensional modeling provides better accurate solution and closely fit with the experimental results. The model can be used as basic tool for accurate simulation of MESFET photodetector for OEIC applications.