Epitaxial ZnSe/epitaxial GaAs interfaces are formed by molecular beam epitaxy and evaluated by several techniques including capacitance-voltage (C-V) measurements. The GaAs surface stoichiometry is systematically varied prior to the nucleation of ZnSe. A dramatic reduction of interface state density occurred when the GaAs epilayer is made As deficient. The ZnSe/GaAs interfaces exhibiting low interface state densities are associated with the presence of an interfacial layer of zincblende Ga2Se3. In situ X-ray photoelectron spectroscopy (XPS) is used to study the nature of the bonding at the interfacial layer. The character of Se 3d core level features from the interfacial region and from separately grown Ga2Se3 epilayers support the identification of the interfacial layer as Ga2Se3.
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