As-rich (2 × 2) surface reconstruction on GaAs(111)A

The atomic structures and the formation processes of the Ga- and As-rich (2×2) reconstructions on GaAs(111)A have been studied. The Ga-rich (2×2) structure is formed by heating the As-rich (2×2) phase, but the reverse change hardly occurs by cooling the Ga-rich surface under the As2 flux. Only when the Ga-rich (2×2) surface covered with amorphous As layers was thermally annealed, the As-rich (2×2) surface is formed. The As-rich (2×2) surface consists of As trimers located at a fourfold atop site of the outermost Ga layer, in which the rest-site Ga atom is replaced by the As atom.