INFLUENCE OF IMPACT IONIZATION ON THE DRAIN CONDUCTANCE IN INAS-ALSB QUANTUM-WELL HETEROSTRUCTURE FIELD-EFFECT TRANSISTORS

Using an InAs-AlSb heterostructure field-effect transistor (HFT) struc ture modified to incorporate an epitaxial p-type GaSb back gate, we me asure the impact ionization current caused by hot electrons in the InA s channel. We show that the impact ionization current is only a small fraction of the deleterious increase in the drain current commonly obs erved in InAs-based transistors, Most of the drain current rise is cau sed by a feedback mechanism in which holes escaping into the substrate act like a positively charged parasitic back gate leading to an incre ase in the electron current flow in the channel by an amount that is l arge compared to the impact ionization current itself, Removal of the impact-generated holes by the epitaxial back gate breaks the feedback loop, and dramatically improves the de characteristics of the devices, and increases the range of usable drain voltages.