Physics of breakdown in InAlAs/n/sup +/-InGaAs heterostructure field-effect transistors

InAlAs/InGaAs heterostructure field-effect transistors (HFETs) have demonstrated a high breakdown voltage in spite of their narrow channel bandgap. To understand this unique feature, the authors have carried out a systematic study in a range of temperatures around room-temperature. They found that for HFETs with gate length L/sub G/=1.9 /spl mu/m, breakdown is drain-gate limited and is a two-step process. First, electrons are emitted from the gate to the insulator. Second, as a consequence of the large /spl Delta/E/sub C/, they enter the channel hot, into the high-field drain-gate region, and immediately relax their energy, causing impact-ionization. This combined mechanism explains all the observations to date regarding off-state breakdown phenomena in InAlAs/n/sup +/-InGaAs HFETs.