Gate current of modulation-doped field-effect transistors

Abstract

We present a new room‐temperature model for modulation‐doped field‐effect transistors and heterojunction insulated gate field‐effect transistors that accounts for effects induced by the gate current at large gate voltages. For large gate currents the quasi‐Fermi levels in the GaAs channel and the AlGaAs barrier layers are different because of the limited electron exchange imposed by the heterojunction band offset. As a consequence, the channel electron concentration for large gate voltages exceeds the value expected for the n‐AlGaAs/GaAs material system in thermal equilibrium. The channel electron capacitance can have two peaks as a function of gate voltage leading to similar structure in the gate voltage dependence of the transconductance. We find good agreement between our calculated and measured gate currents as a function of the gate voltage.