COMPOSITIONAL ELASTIC DOMAINS IN EPITAXIAL LAYERS OF PHASE-SEPARATING SEMICONDUCTOR ALLOYS

The global stability of a homogeneous III-V semiconductor alloy in an epitaxial film on the [001] substrate is examined with respect to an arbitrary modulation of alloy composition. The coherent phase separation in epitaxial films of unstable alloys is shown to result in the formation of structures with periodic modulations of alloy composition along the [100] (or [010]) direction of the lowest stiffness in the substrate plane. The equilibrium concentration profile is governed by the interplay of the chemical and the elastic energies. The amplitude of the composition modulation is found to be maximum at the free surface and to decay in the depth of the epitaxial film. The phase diagram of the epitaxial alloy stability is calculated for a GaAs1-cSbc alloy.