Pseudo two-dimensional simulation of a three heterojunction GaAs/AlGaAs MODFET

A new model is presented for the simulation of the d.c. characteristics of three heterojunctions AlGaAs/GaAs Field Effect Transistors. The dependence of the carrier densities in the GaAs wells and in the doped AlGaAs layers is derived as a function of gate voltage by analytical resolution of Schrödinger equation and numerical resolution of Poisson's equation using Fermi-Dirac statistics. The simulated d.c. characteristics are obtained by numerical integration of the current density from source to drain and include the source and drain access resistances. The comparison between experimental measurements and calculated results for both long (L_g = 20 μm) and short (L_g = 2 μm) gate lengths MODFETs is excellent and demonstrates the validity of the model to optimize the device parameters. The influence of various parameters such as the AlGaAs layer thickness and electron velocity in the inverted well on the device performance is numerically simulated for a 1 μm gate length device. Their effect on the transistor characteristics such as transconductance and maximum drain current is discussed.