Relationship between the lateral length and thickness of the platelets in naturally occurring strained layer superlattice structures

The molecular beam epitaxial growth of InAs_0.5Sb_0.5 onto (001) surfaces below 430°C results in the formation of a "natural" strained layer superlattice (n-SLS). Transmission electron micrographs of 〈110〉 cross sections showed the existence of two different alloy compositions that formed a tetragonally distorted interleaved platelet structure in which the interfaces were highly regular and ran approximately parallel to the growing surface. It is found that the structure of the n-SLS can be changed systematically by carefully controlling the InAs_0.5Sb_0.5 growth conditions. A simple relationship is derived relating the lateral size of the platelet to its thickness that is found to hold experimentally for n-SLS structures. It is suggested that the n-SLS structure occurs because it corresponds to the minimum free energy configuration of the growing crystal. A similar formalization has been applied to periodic modulations in other material systems.