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) structure modified to incorporate an epitaxial p-type GaSb back gate, we measure the impact ionization current caused by hot electrons in the InAs channel. We show that the impact ionization current is only a small fraction of the deleterious increase in the drain current commonly observed in InAs-based transistors. Most of the drain current rise is caused by a feedback mechanism in which holes escaping into the substrate act like a positively charged parasitic back gate leading to an increase in the electron current flow in the channel by an amount that is large 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 DC characteristics of the devices, and increases the range of usable drain voltages.