Observation of a new ordered phase in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$As alloy and relation between ordering structure and surface reconstruction during molecular-beam-epitaxial growth

A new phase with spontaneous atomic ordering on the sublattice is found in ${\mathrm{Al}}_{0.48}$ ${\mathrm{In}}_{0.52}$As grown on exact (001)InP substrate by molecular-beam epitaxy. The atomic arrangement is a periodic sequence of {111}A planes in a unit of ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$/${\mathrm{Al}}_{\mathit{y}}$ ${\mathrm{In}}_{1\mathrm{-}\mathit{y}}$/${\mathrm{Al}}_{\mathit{z}}$ ${\mathrm{In}}_{1\mathrm{-}\mathit{z}}$ on the group-III sublattice. The surface reconstruction during growth is (2×3). A CuPt-type ordered phase is observed in crystals grown at higher temperatures, where the reconstruction is (2×1). This correlation with respect to periodicity and direction between the reconstructions and the types of ordered phase unequivocally demonstrates that surface reconstruction plays a central role in ordered structure formation. Band-gap reductions of ∼80 and ∼30 meV are observed for the new ordered phase and the CuPt-type phase, respectively.