Study of Initial Growth Layer of GaSb on Si(111) by Scanning Tunneling Microscopy

The initial growth layer of GaSb on a Si(111) surface has been studied by scanning tunneling microscopy. After the simultaneous deposition of Ga and Sb atoms at 0.85 and 1.45 monolayers, respectively, Sb/Si(111)-$2{\times}1$ and -$\sqrt{3}{\times}\sqrt{3}$-R30° structures were formed on a large area of the Si(111) surface. In addition, the protrusions of the cross-hatch pattern, which was higher than that of the Sb/Si(111) structures by a bilayer height, were observed. The pattern area is suggested to correspond to the initial growth layer of GaSb. Three types of layer domains were observed. These domains are formed because of the strain caused by the lattice mismatch between GaSb and Si. Based on both cases of group-III and -V polar surface structures, the atomic structural models of these domains are proposed: one domain is a layer with strain relaxation, formed by the reconstruction of on-top atoms; the second is a layer formed on the reconstructed Si surface; and the third is a layer with uniaxial strain relaxation. Three-dimensional hut-shaped islands were observed to form infrequently on the local surface area. A cross-hatch pattern similar to the initial growth layer was observed on the facets of these islands. It is suggested that the islands are composed of GaSb crystals. An initial growth layer of GaSb was observed around some of the islands. From these results, we speculate that the GaSb dot crystals grow epitaxially on the initial layer.