Continuous heterostructure field effect transistor model

A continuous model for heterostructure field effect transistors (HFETs), suitable for circuit simulation and device characterization, is proposed. The model is based on the analytical solution of the two-dimensional Poisson´s equation in the saturation region. The HFET saturation current and saturation voltage are determined by differentiating the output characteristics in a unified and unambiguous way. These results are used for a systematic extraction of device and process parameters, such as the threshold voltage, effective electron saturation velocity and mobility, drain and source series resistances, effective gate length, and characteristic length for channel length modulation. The deduced values agree well with other independent measurements. The results of experimental studies of HFETs with nominal gate lengths of 1.0, 1.4, 2.0, and 5.0 micron are reported. A large short-channel effect is observed for the 1.0 micron gate HFET. The gate length dependences of the device parameters uniquely determined by the method reveal that the effective gate length in these self-aligned structures is approximately 0.25 micron shorter than the nominal gate length