Calculations were made of the surface energy change that was due to step formation that was caused by misfit dislocation nucleation in thin-film semiconductor heterostructures. It was found that the surface energy change was negative for a compressive misfit stress in the hetero-epitaxial film, but was positive for a tensile misfit stress. This was contrary to the classical model, where the step formation energy was always positive and was independent of the sign of the misfit. The calculated energy change was qualitatively explained by counting the number of dangling bonds at the surface. By using atomistic simulations, calculations were made of the critical thickness for dislocation nucleation. These took account of the surface energy change. It was found that the critical thickness varied from 4nm, for Ge films on (001)Si substrates, to 6nm for Si films on (001)Ge substrates (for the same misfit).

M.Ichimura, J.Narayan: Philosophical Magazine A, 1995, 72[2], 297-304