Surface segregation of third-column atoms in group III-V arsenide compounds: Ternary alloys and heterostructures

Abstract

We report a systematic study of the segregation of third-column elements involved in group III-V arsenide structures to their (100) surface. The surface composition is obtained by in situ electron spectroscopies, on special structures built by molecular-beam epitaxy. In ternary alloys, an important surface enrichment in one of the third-column components is most often observed, leading to a near-binary surface. Heterojunctions between two given binary materials A and B are abrupt or not in composition, depending on the growth sequence (A grown on B or B grown on A): for one sequence, the top monolayer of the base material is gradually distributed in the growing overlayer. All these behaviors can be summarized by tendencies to surface segregation following In>Ga≥Al, and by segregation efficiencies that are either near zero or near unity depending on the way structures are built. The application of standard models to the segregation isotherms for ternary alloys yields segregation energies of 0.1–0.2 eV. The physical origin for the segregation process and its consequences on interface roughness along the growth axis are discussed.