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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)-2×1 and -√3×√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.

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GaSb layers grown on a Ga-terminated Si(111) surface have been studied by ultrahigh-vacuum scanning tunneling microscopy. Two types of two-dimensional islands are locally formed on the initial GaSb growth layer on Ga/Si(111)-√3×√3 at a Ga coverage of about 1.2 ML and a Ga/Sb ratio of 4.4. The first type of island is higher than the initial growth layer by a bi-atomic step height. The triangular protrusions on this island correspond to those on the initial GaSb layer. A hexagonal pattern that is higher than the initial growth layer by double the height of the bi-atomic step is observed on the second type of island. Protrusions in the pattern are arrayed at approximately 0.8 nm intervals, which is the distance between twice the unit cell length of Si and GaSb, along the intrinsic direction of the Si(111) surface. Defect lines similar to the misfit dislocation network are observed on the island. These results suggest that the island corresponds to the slightly lattice-relaxed GaSb third layer. A three-dimensional island is formed on the third GaSb layer as GaSb coverage increases. These results indicate that the third GaSb layer is the nucleation site of the three-dimensional GaSb island on Si(111).

The Ga adsorption structures on the Ni-induced Si(100) surface have been studied by scanning tunneling microscopy. The protrusions, which are different from Ga ad-dimer, are observed on the dimer vacancy lines (DVLs) after the Ga ad-dimers cover the Si region. The amount of protrusions increases as Ga coverage increases and these protrusions occupy the DVLs at about 0.50 monolayer. The type of protrusions on the DVLs is similar to the precursor state of the Ga clusters. Islands of different sizes are formed locally on the steps and terraces as coverage increases. Small islands are distributed evenly on the terraces after annealing the surface at 200 °C, whereas large islands are formed again at 400 °C. The changes in the distribution of the islands are associated with the nuclei sites on the DVLs and the transformation of the surface structure.