Abstract

The properties of alloy semiconductors are influenced by the state of order of the materials. Some properties, such as the liquidus and solidus curves, are relative insensitive but others are strongly affected. We first demonstrate which aspects of bonding interaction mechanisms impact the correlation state. We then deduce the effect of the correlation state on liquids and solidus curves, on surface segregation, and on vacancy densities. Surface segregation is a concentration variation of the alloy constituents away from surfaces, and is driven by Schottky vacancy-free energy differences between the constituents in the bulk and on a surface. The segregation profile for alloys equilibrated above a critical spinodal transition temperature exhibits a monatomic variation decaying over a few atomic layers from the surface to the bulk value. However, long-range concentration oscillations are predicted below the critical temperature. These oscillations may account for the long-range order observed in some MBE- and MOCVD-grown alloys (e.g., InPSb). The total free energy of this new ordered phase lies between that of a homogeneous but highly correlated alloy and that of a spinodally decomposed alloy. The phase, if it exists, would be locked into its metastable state by the presence of the surface. Boundary conditions at the interface between the epitaxial layer and the substrate would also affect the results.

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