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

InAlAs/n⁺-InGaAs HFET´s on InP have demonstrated a high breakdown voltage in spite of the narrow bandgap of the InGaAs channel. In order to understand this unique feature, we have carried out a systematic temperature-dependent study of off-state breakdown. We find that off-state breakdown at room-temperature is drain-gate limited and that the breakdown voltage shows a negative temperature coefficient. Based on these and other findings, we propose that off-state breakdown is a two-step 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 through impact-ionization. This combined mechanism explains our experimental observations that off-state breakdown in InAlAs/n⁺ -InGaAs HFET´s depends both on channel and insulator design. Our findings are relevant to other InAlAs/InGaAs HFET´s, such as the MODFET, as well as HFET´s based on other narrow-bandgap materials