The surface states of ideal, (100) cation- and anion-terminated surfaces of ${\mathrm{Hg}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Cd}}_{\mathrm{x}}$Te (x=0, 0.2, 0.5, 0.8, 1.0) have been determined by use of the site-dependent coherent-potential approximation (SDCPA) for the alloy. Alloy effects are more important for localized states than for well-extended states and are greatly enhanced for states that are sensitive to the cation sites and localized to a cation surface. In the alloy, the localized states sensitive to the disorder have the character of the alloy constituents rather than of some average, effective constituent. The ideal cation surface has HgTe- and CdTe-like surface-state bands between the valence and conduction bands but no virtual-crystal-related surface-state features in this energy range. Both constituentlike bands exist for each alloy composition except x=0 or 1.0. Anion surface states and back-bonded surface states occurring below the valence-band edge do not exhibit this bimodal character because these states are less sensitive to the cation sites. The coherent-potential-approximation (CPA) self-energy at a cation-surface site is also very different from those in the bulk or near anion surfaces as a result of the surface-enhanced alloy effects. For comparison with the SDCPA, we also present results obtained with the virtual-crystal approximation and with the bulk CPA (same self-energy at all sites). Only the SDCPA yields a qualitatively correct description of all the states considered.

• Received 6 November 1986

DOI:https://doi.org/10.1103/PhysRevB.35.5547