Two-dimensional transient simulation of the high electron mobility transistor

We develop a model for the High Electron Mobility Transistor (HEMT) which simulates conduction both inside and outside the quantum-well subbands and includes hot electron effects within the framework of average-energy-dependent parameters in macroscopic transport equations. At 77K we see significant velocity overshoot and bulk conduction. From transient simulations it is seen that the current-switching speed is a function of the electron transit time. From this we conclude that the advantage of the excellent conduction in the quantum well is not in a high saturation velocity at pinch-off but rather in a low access resistance. We also conclude that for the HEMT current saturation cannot be explained in terms of a velocity saturation mechanism at the drain edge of the gate. Finally, from steady-state calculations at 300K, we find that although velocity overshoot is reduced, the basic effects are similar to those seen at 77K.