First-principles calculation of the effect of strain on the diffusion of Ge adatoms on Si and Ge (001) surfaces

First-principles calculations are used to calculate the strain dependencies of the binding and diffusion-activation energies for Ge adatoms on both Si(001) and Ge(001) c(4×2) reconstructed surfaces. Our calculations reveal that over the range of strains typically sampled during quantum dot self-assembly (0 to 1 % compressive strain) the binding and activation energies on a strained Ge(001) surface increase and decrease., respectively, by 0.21 eV and 0.12 eV. For a growth temperature of 600 °C, these strain-dependencies give rise to a 16-fold increase in adatom density and a 5-fold decrease in adatom diffusivity in the region of compressive strain surrounding a Ge island with a characteristic size of 10 nm lying on top of a Si substrate covered by a Ge wetting layer.