A Analytical Model for High Electron Mobility Transistors and its Application to Inverse Modeling

A new model for the high electron mobility transistor is presented in this thesis. The model is based on an analytical function that describes the free electron concentrations in the two dimensional electron gas and in the AlGaAs layer. Besides accounting for the AlGaAs conduction, the model includes the effect of mobility degradation, channel length modulation in the saturation region and the parasitic resistances. The model results in closed form expressions for the current, transconductance, output conductance, gate capacitance and unity current gain frequency. A comprehensive treatment of the gate capacitance is presented which helps delineate the difference between the different definitions that appear in the literature. The capacitance model assumes that the gate voltage controls the two dimensional electron gas concentration as well as the density of the neutralized donors and the free electrons in the AlGaAs layer. The concept of inverse modeling is applied to the high electron mobility transistor to determine the device structure and physical parameters from the measurement of the maximum transconductance at a given operating gate voltage. The theoretical predictions of the model developed are compared with the experimental data and shown to be in good agreement over a wide range of bias conditions.