Surfactant-induced bond strengthening in As-grown film surfaces

The role of surfactant (Sb) in the two-dimensional (2D) growth of Ge films on Sb-adsorbed Si(lll) surfaces is investigated using the discrete variational (DV) - X alpha cluster method. The results show that the Sb surfactant strengthens bonds between Ge atoms of the film surface, to the extent of those in bulk Ge, and enables them to realize an sp(3)-like configuration. This indicates why the critical thickness is increased in this system: the surfactant-induced bond strengthening renders the film surface hard like that of bulk Ge, induces dislocations to nucleate at the surface; and enables the Ge film to grow in a defect-free state, as expected based on the self-annihilation mechanism proposed by Horn-von Hoegen et al. [M. Horn-von Hoegen et al. Phys. Rev. Lett. 67 (1991) 1130].