Ab initiostudy of the Bi-coveredGaAs(111)Bsurface

Abstract

An ab initio theoretical study has been performed, within the local-density approximation and the pseudopotential method, of the atomic geometry, electronic structure, and energetic stability of the Bi-covered $\mathrm{GaAs}(111)B$ surface. The results obtained support the stability of the $c(4\ifmmode\times\else\texttimes\fi{}2)$ reconstruction observed experimentally by McGinley et al. [Appl. Surf. Sci. 152, 169 (1999)], for a Bi coverage of 0.75 monolayer, with the Bi trimers aligned along the $[112\ifmmode\bar\else\textasciimacron\fi{}]$ direction. The Bi trimers are found to be energetically more favorable in the ${T}_{4}$ sites rather than in the ${H}_{3}$ sites. The electronic-band-structure calculations indicate that the surface is semiconducting in nature. The highest occupied surface state is resonant with the GaAs-bulk valence band, and is localized on the unbonded second-layer As atoms. The lowest unoccupied state is mainly localized on the Bi trimers, and exhibits a charge-density overlap between neighbor Bi trimers. In general, the electronic band structure, atomic geometry, and simulated scanning tunnel microscope images of the Bi-covered $c(4\ifmmode\times\else\texttimes\fi{}2)$ surface show similarities with the Sb-covered (3\ifmmode\times\else\texttimes\fi{}8) and As-covered (2\ifmmode\times\else\texttimes\fi{}2) surfaces.