Valence-band structures of III-V compounds and alloys—Bond-orbital and coherent-potential approximations

The bond-orbital model (BOM) and the coherent-potential approximation (CPA) are used to study the valence-band structures of the III-V compound semiconductors GaP, GaAs, GaSb, InP, InAs, and InSb and their alloys. All the third-neighbor bond interactions are included, but the main outstanding defects in the BOM found by previous authors remain. However, the model reproduces the major structure of the observed densities of states. The BOM is especially convenient for alloys because it effectively isolates the important disorder parameters and facilitates the execution of CPA. The model's parameters are deduced by fitting to the photoelectric thresholds and x-ray photoemission spectra. We found that the most interesting CPA results are not the densities of states usually studied but are the more detailed band properties like energy shifts, effective masses, alloy scattering, and optical-absorption-line broadening. This work provides a basic understanding of the effect of alloy disorder on the nonlinear concentration dependence of the energy at the top of the valence band and line broadening of the fundamental optical gap $E_0$.