Length mismatch in random semiconductor alloys. II. Structural characterization of pseudobinaries

We have made an extensive study of the pseudobinary semiconductor compounds (${\mathit{A}}_{1\mathrm{-}\mathit{x}}$ ${\mathit{B}}_{\mathit{x}}$)C, which includes both the III-V and the II-VI alloys. We use a Kirkwood model with all parameters derived from the elastic constants of the pure materials. It is shown that the mean lengths are linear in the composition x if the force constants for the two pure materials AC and BC are the same. We have derived analytic results for the mean lengths of AC and BC bonds and for their widths in the preceding paper. We construct an effective-medium theory for cases in which there is disorder in the force constants. This effective-medium theory is found to be in good agreement with the results of computer simulations of the same models. Mean values for the next-nearest-neighbor lengths are also given, and found to agree with extended x-ray-absorption fine-structure results.