Monte Carlo simulation of impact ionization and light emission in pseudomorphic HEMTs

We present theoretical investigations of electrical and optical phenomena in the near breakdown regime of pseudomorphic HEMTs. The main effect of the drain current enhancement is found to be a parasitic bipolar effect due to holes, created by impact ionization, which accumulate in the substrate. Calculated electroluminescense spectra of holes, radiatively recombining with electrons in the source-sided channel, exhibit transitions which are allowed due to the bias-induced band bending of the channel. The calculated electroluminescence of the gate-source region agrees well with available experimental data. We predict that the hole accumulation in the source side of the channel region takes place on a time scale of ∼150 ps, thus allowing a direct time-resolved experimental observation.