SURFACE RECONSTRUCTIONS AND SURFACE ENERGIES OF MONOLAYER-COVERAGE CATION-TERMINATED GA0.5IN0.5P(001) SURFACES

Using the first-principles pseudopotential method we have studied the fully covered cation-terminated (001) surfaces of Ga0.5In0.5P alloys. We find that among several possible Ga and In surface patterns (within a 2 x 2 unit cell), the one corresponding to CuPt-like bulk ordering is stabilized by approximately 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.