Initial domain structure of GaAs thin films grown on Si(001) substrates

The initial domain structure of GaAs films grown on several Si(001) surfaces is investigated using X-ray standing waves. GaAs/Si(001) samples, 4 ML thick, grown on three different Si substrates were used: an epitaxial Si surface (ESS), a mechanochemically polished surface (MCP), and a mechanochemically polished surface with plasma cleaning (plasma MCP). The domain ratio ambiguousness due to the film thickness is avoided by observing independent Bragg reflections of Si substrates. The results of X-ray standing wave measurement reveal that all GaAs films have double domain structures at the initial stage, even though final domain structures are single. The ratio of the two domains was almost 1 : 1 on the MCP surface, 6:4 on the ESS surface, and 4.5:5.5 on the plasma MCP surface. The dominant GaAs domains on the ESS and plasma MCP surfaces were the same as those obtained on thicker GaAs films. This suggests there is a rapid decrease in the GaAs domain during the early stages of growth on an ESS and plasma MCP surfaces.