New continuous heterostructure field-effect-transistor model and unified parameter extraction technique

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 a two-dimensional Poisson equation in the saturation region. The HFET saturation current and saturation voltage have been experimentally determined by differentiating the output characteristics in a unified and unambiguous way. The results are used for the systematic extraction of device and process parameters. The deduced values agree well with other independent measurements. The results of experimental studies of HFETs with nominal gate lengths of 1, 1.4, 2, and 5 μm are reported. The models and techniques presented here are successfully applied to all these devices. A large short-channel effect is observed for the 1-μm-gate HFET. The gate length dependences of the device parameters determined by the method reveal that the effective gate length in the self-aligned structures is approximately 0.25 μm shorter than the nominal gate length