Characterization of hole transport phenomena in AlGaAs-InGaAs HEMT´s biased in impact-ionization regime

Mastering hot-electron and impact-ionization effects is of crucial importance for power AlGaAs-InGaAs pseudomorphic HEMT design. Spectroscopic analysis of electroluminescence (EL) has been extensively used to characterize hot carrier effects in MESFETs and HEMTs. In this paper, we analyse carrier transport phenomena occurring in pseudomorphic AlGaAs-InGaAs HEMTs biased in the on-state impact-ionization regime by means of EL. We confirm the presence in the EL spectra of pseudomorphic HEMTs of a dominant contribution at high energies due to electron-hole recombination, and identify a composite peak due to the recombination of cold carriers. We analyze the recombination peak using a high-resolution monochromator, which reveals the fine structure due to transitions between electron and hole subbands in the channel quantum well, thus providing useful data on the properties of the InGaAs HEMT channel. The EL data are modelled by means of a self consistent tight binding calculation. We observed that the fine structure of the recombination peaks is not influenced by the drain-source voltage, thus suggesting that recombination occurs between nonenergetic electrons and holes in the gate-source region, as observed by Shigekawa et al (1995) for InAlAs-InGaAs HEMTs on InP. We also show, for the first time, that at high V/sub DS/ and electric field, significant recombination occurs in the AlGaAs layers, which demonstrates the real space transfer of both electrons and holes.