Model for modulation doped field effect transistor

A model describing and characteristics of modulation doped FET\´s is proposed. The model takes into account the change in the Fermi energy with the gate voltage. At high two dimensional electron concentrations, the equations of the model for the charge control by the gate voltage become similar to the equations of the charge control model where the thickness d of AlGaAs layer should be substituted by d + Δ d and Δ d is the effective width of the potential well (≃ 80 Å). Another important prediction of the model is the existence of the "subthreshold" current. A very good quantitative agreement is obtained with our experimental curves using the measured values of the low field mobility and the source resistance.