Surface reconstructions and surface energies of monolayer‐coverage cation‐terminated Ga_0.5In_0.5P(001) surfaces

Using the first‐principles pseudopotential method we have studied the fully covered cation‐terminated (001) surfaces of Ga_0.5In_0.5P alloys. We find that among several possible Ga and In surface patterns (within a 2×2 unit cell), the one corresponding to CuPt‐like bulk ordering is stabilized by ∼100 meV per surface atom. This structure has been observed experimentally in thick films, yet is known to be bulk unstable. The stability of a CuPt‐like surface layer is related to electronically driven surface reconstructions—dimerization, buckling, and tilting—which are discussed in detail.