PHYSICS OF BREAKDOWN IN INALAS N(+)-INGAAS HETEROSTRUCTURE FIELD-EFFECT TRANSISTORS/

InAlAs/n(+)-InGaAs HFET's on InP have demonstrated a high breakdown vo ltage in spite of the narrow bandgap of the InGaAs channel. In order t o understand this unique feature, we have carried out a systematic tem perature-dependent study of off-state breakdown. We find that off-stat e breakdown at room-temperature is drain-gate limited and that the bre akdown voltage shows a negative temperature coefficient. Based on thes e and other findings, we propose that off-state breakdown is a two-ste p process. First, electrons are injected by thermionic-field emission from the gate to the insulator, Second, electrons enter into the high- field drain-gate region of the channel hot, and relax their energy thr ough impact-ionization. This combined mechanism explains,our experimen tal observations that L off-state breakdown in InAlAs/n(+)-InGaAs HFET 's depends both on channel and insulator design, Our findings are rele vant to other InAlAs/InGaAs HFET's, such as the MODFET, as well as HFE T's based on other narrow-bandgap materials.