Surface treatment of the GaSb cap layer is investigated for the gate operation of InAs/AlGaSb heterostructures with an Al 2O 3 insulating layer grown by atomic layer deposition. We show that dilute HCl treatment for only 10 s effectively removes the electron trap states at the GaSb/Al 2O 3 interface and greatly improves the gate operation. In contrast, HCl treatment followed by water rinse results in adverse effects. Using an equivalent circuit model, we deduce the interface trap state density for the no-treatment case to be D it ∼ 10 13cm -2eV -1, which is reduced to well below 10 12 cm -2eV -1 by the HCl treatment. Our data also show that deep donor states in the AlGaSb barrier impede the gate operation and cause gate hysteresis.
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