Monte Carlo simulation of 0.35-μm gate-length GaAs and InGaAs HEMTs

A first-principles theoretical comparison of the performances of identical Al_0.32Ga_0.68As/GaAs and Al_0.15Ga_0.15As/In_0.15Ga_0.85 As/GaAs pseudomorphic HEMTs based on an ensemble Monte Carlo simulation coupled with a two-dimensional Poisson solver is presented. The Monte Carlo calculations incorporate the full physics of the device operation. As a test of the accuracy with which the calculations successfully model a real device, the calculated current-voltage characteristic of the pseudomorphic device is first compared to recent experimental measurements made on a comparable structure, showing excellent agreement over a full range of gate and drain biases. The device performance as measured in terms of the transconductance, cutoff frequency, and current-voltage characteristics of both devices can then be compared as a function of gate and drain bias. It is found that the pseudomorphic HEMT outperforms the conventional GaAs/AlGaAs device by approximately a factor of two in the above-mentioned criteria. The greatly improved performance of the pseudomorphic HEMT over the GaAs device stems predominantly from greater confinement of the electrons within the high-mobility two-dimensional system, higher electron drift velocity, and greater gamma valley confinement