Abstract
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 similar to 150 ps, thus allowing a direct time-resolved experimental observation. (C) 1999 Elsevier Science B.V. All rights reserved.