Analytic simulation of impact ionization in InAlAs/InGaAs HFET's

A physical model for InP-based HFET including velocity overshoot and impact ionisation effects has been developed using a novel bias dependent velocity approach. This approach bases on a fit-function to data obtained by Monte-Carlo-simulations and has been carefully transferred to the special conditions in HFET-channels. Since impact ionization occurs at high drain-bias, the variation of the free surface potentials due to selective recess etches and scattering of electrons into the barrier material as predicted by Monte-Carlo-simulations have been taken into account in the evaluation of the quasi-2D-potential and field distribution. However, although the physical understanding is emphasized and only explicit analytic formulas of simple nature will be presented, the simulated output and input characteristics well mirror measured data.