OBSERVATION OF A NEW ORDERED PHASE IN ALXIN1-XAS 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 Al0.48In0.52As 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 AlxIn1-x/AlyIn1-y/AlzIn1-z on the group-III sublattice. The surface reconstruction during growth is (2x3). A CuPt-type ordered phase is observed in crystals grown at higher temperatures, where the reconstruction is (2 x 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 approximately 80 and approximately 30 meV are observed for the new ordered phase and the CuPt-type phase, respectively.