Surface-enhanced alloy effects in ${\mathrm{Hg}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Cd}}_{\mathrm{x}}$Te: (100) surface states and the site-dependent coherent-potential approximation

The density of states for ideal (100) cation- and anion-terminated surfaces of ${\mathrm{Hg}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Cd}}_{\mathrm{x}}$Te (x=0.5) have been determined with a site-dependent coherent-potential approximation for the alloy. Alloy effects are greatly enhanced at a cation surface. The cation-surface density of states exhibits HgTe- and CdTe-like surface-state bands with no virtual-crystal–related surface-state features. This bimodal character does not appear in the bulk or anion surface density of states. Similarly, the self-energy at a cation surface site is very different from those in the bulk or near-anion surfaces.