First-principles study of strain stabilization of Ge(105) facet on Si(001)

Using the first-principles total energy method, we calculate surface energies, surface stresses, and their strain dependence of the Ge-covered Si (001) and (105) surfaces. The surface energy of the Si(105) surface is shown to be higher than that of Si(001), but it can be reduced by the Ge deposition, and becomes almost degenerate with that of the Ge/Si(001) surface for three-monolayer Ge coverage (the wetting layer), leading to the formation of the {105}-faceted Ge hut. The unstrained Si and Ge (105) surfaces are unstable due to the large tensile surface stress originated from the surface reconstruction, but they can be largely stabilized by applying an external compressive strain, such as by the deposition of Ge on Si(105). Our study provides a quantitative understanding of the strain stabilization of Ge/Si(105) surface, and hence the formation of the {105}-faceted Ge huts on Si(001).