Two-dimensional transient simulation of an idealized high electron mobility transistor

A model is developed for the high electron mobility transistor (HEMT) in which are included both hot-electron effects and conduction outside the quantum subband system using hydrodynamic-like transport equations. With such a model the significance of the various physical phenomena involved in the operation of the HEMT can be assessed. Results are calculated with a two-dimensional numerical technique for both steady-state and transient operation. For a 3-micron device at 77 K, a transconductance of 450 mS/mm is determined along with a current-switching speed of 6 ps, and a capacitive charging speed of 4 ps/fanout gate which corresponds to the performance measured by other workers. It is also seen that electronic heating, velocity overshoot, and conduction outside the quantum well are significant near the pinchoff point. It is concluded that the advantage of HEMT is twofold. The excellent conduction in the quantum well results in a low access resistance, and the low impurity concentration in the GaAs results in optimum overshoot effects.