COMPOSITIONAL ELASTIC DOMAINS IN EPITAXIAL LAYERS OF PHASE-SEPARATINGSEMICONDUCTOR 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 a rbitrary modulation of alloy composition. The coherent phase separatio n in epitaxial films of unstable alloys is shown to result in the form ation of structures with periodic modulations of alloy composition alo ng the [100] (or [010]) direction of the lowest stiffness in the subst rate plane. The equilibrium concentration profile is governed by the i nterplay of the chemical and the elastic energies. The amplitude of th e composition modulation is found to be maximum at the free surface an d to decay in the depth of the epitaxial film. The phase diagram of th e epitaxial alloy stability is calculated for a GaAs1-cSbc alloy.