Two-dimensional numerical analysis of the high electron mobility transistor

We develop a two-dimensional model for the high electron mobility transistor (HEMT) including conduction outside the quantum well. The model uses the continuity and power balance moment equations for both inside and outside the well, with electron concentration and average energy as dependent variables, and with parameters determined by Monte Carlo simulation. We show that conduction outside the well is dominant in the "pinchoff" region and that consequently the speed advantage of the HEMT over conventional devices does not arise from high saturation velocities in the quantum well but rather from a lower access resistance as suggested by a velocity profile calculation. It is further demonstrated that several effects which are unimportant in conventional FET\´s are of significance in the HEMT. Among these effects are electronic heat conduction and to some extent real space transfer.