A new and simple model for GaAs heterojunction FET gate characteristics

The gate current-voltage characteristics for modulation-doped field-effect transistors (MODFETs) and heterostructure insulated-gate field-effect transistors (HIGFETs) are described using a simple model. This model, which is physically realistic, consists of two Schottky diodes in series: one is a metal-semiconductor (AlGaAs) Schottky diode and the other is an equivalent Schottky diode due to the heterojunction between the AlGaAs and GaAs. A novel technique is developed to characterize the parameters used for this model. The model is used to estimate the effective electron temperature in the channel close to the drain for MODFETs. The estimated electron temperature with 1 V drain-to-source voltage is as high as 80°C at room temperature. Very good agreement between the calculated and measured results is obtained. This model and characterization technique are also suitable for other heterojunction FETs such as quantum-well MODFETs, etc