Simulation of a GaAs MESFET including velocity overshoot: an extended drift-diffusion formalism

Numerical simulations are described for GaAs MESFETs. They are based on an extended drift-diffusion equation formalism which allows for the inclusion of the velocity overshoot effect. The overshoot correction term which augments the drift-diffusion current equation is proportional to the gradient of the local electric field. The proportionality constant has been calculated by Monte Carlo methods as a function of the electric field. The model developed solves the extended drift-diffusion current continuity equation and Poisson´s equation over a two-dimensional grid using the method of finite differences. Simulations for normally-on and normally-off devices with gate lengths of 0.2, 0.5, and 1.0 mu m are compared with published Monte Carlo calculations. The calculated drain currents and average electron velocities in the device channel are in excellent agreement. The extended drift-diffusion formalism is useful and easy to implement for modeling field-effect transistors with submicron feature size.<>