Sb and Bi on GaAs(110): Substrate-stabilized overlayer structures studied with scanning tunneling microscopy

Abstract

The growth structures for Sb and Bi films on GaAs(110) have been studied for thicknesses of 0.5--50 monolayers (ML) with annealing to temperatures as high as 600 K. Antimony films exhibit layered structures with \ensuremath{\sim}6-\AA{} heights but also disordered surface features for coverages up to \ensuremath{\sim}10 ML when grown at 300 K. Annealing to 500 K produces orientationally ordered films that contain grains with striped domain walls and two differently oriented superstructures. These superstructures can be explained in terms of a Moir\'e effect in which the 〈001〉 direction of the pseudocubic Sb(110) plane is rotated by +7\ifmmode^\circ\else\textdegree\fi{} or-7\ifmmode^\circ\else\textdegree\fi{} from the substrate [11\ifmmode\bar\else\textasciimacron\fi{}0] direction. Sb undergoes a semiconductor-semimetal transition when the film thickness reaches \ensuremath{\sim}15 \AA{}. By 20-ML deposition, the ability of the substrate to dictate surface structure is lost. Films grown at 300 K are polycrystalline with randomly oriented basal planes. Annealing to 600 K creates large crystallites with basal planes parallel to the substrate surface. For Bi overlayers on GaAs(110), the first layer is epitaxial but two-dimensional islands form on the 1\ifmmode\times\else\texttimes\fi{}1 layer at 300 K. These islands are \ensuremath{\sim}7 \AA{} in height and exhibit two differently oriented superstructures. As for Sb, this superstructure reflects a Moir\'e effect. For Bi/GaAs, the 〈001〉 direction of the Bi pseudocubic (110) plane is rotated by +10\ifmmode^\circ\else\textdegree\fi{} or -10\ifmmode^\circ\else\textdegree\fi{} from the substrate [11\ifmmode\bar\else\textasciimacron\fi{}0] direction. The islands coalesce to form large, highly anisotropic crystallites having a periodic superstructure at 4-ML coverage. Bi crystallites are formed after 50-ML deposition at 300 K with elongation along the substrate [11\ifmmode\bar\else\textasciimacron\fi{}0] direction.