Large-signal modeling of gallium-arsenide field-effect transistors

A new large-signal, analytic model for the Gallium Arsenide, Metal-Semiconductor Field-Effect Transistor (MESFET) has been developed. The new device model is embedded into a circuit simulation program based on the Harmonic Balance Method to form a Computer-Aided Design (CAD) tool for the analysis of nonlinear microwave FET circuits. The new MESFET model is a physical model and has two unique features: (1) It allows for arbitrary doping profiles in the conducting channel of the MESFET and thus is suitable for the study of large-signal performance of ion-implanted and buried-channel MESFET's. (2) It accounts for charge accumulation in the channel near the drain electrode at large drain-source voltages in a manner consistent with the Poisson equation and global charge neutrality. This study suggests that charge accumulation phenomenon can be significant for devices with submicron gate lengths. In addition to the mentioned features, the model also takes into consideration the 'velocity vector rotation' phenomenon and assumes a smooth transition between the depletion region and the conducting channel of the MESFET. The results of the model are verified with experimental data on three microwave power MESFET's. DC, small-signal and large-signal ac parameters of the three transistors are calculated and shown to be in good agreement with the measured data. The new CAD tool is also used to study a monolithic C-band power MESFET amplifier.