The electric and photoresponse characteristics of Ge/ZnSe heterojunctions

Wide band gap II-VI compounds deposited epitaxially upon semiconducting substrates have possible applications as solid-state infra-red detectors and imaging devices. The Ge/ZnSe heterojunction has been prepared by vacuum evaporation of epitaxial layers of zinc selenide on to orientated, single crystal, p-type, germanium substrates. Measurements have been made of the electrical characteristics, capacitance properties and photoresponse of these junctions. From these measurements a realistic band model has emerged involving intrinsic and extrinsic defects present in the bulk and interfacial region of the zinc selenide. The data presented suggest that a Mott-type barrier rather than a Schottky barrier is present at the germanium-zinc selenide interface. Techniques are described for reducing the magnitude of this Mott barrier and the resulting change in the physical properties and band structure are discussed.