Mechanisms of defect formation near to the surface ledges of a diamond cubic crystal, which was subjected to compressive strain parallel to the surface, were investigated with regard to dislocation nucleation in SiGe/Si(100) hetero-epitaxial thin films under surface diffusion conditions. This study followed previous calculations of dislocation formation at surface ledges, and controlled annealing experiments on the evolution of a SiGe/Si(100) film from an atomically flat, defect-free, surface morphology to give an undulating surface having cusp-like surface features and exhibiting dislocation formation in the cusp valleys. Upon subjecting such films to high-temperature annealing, there was nucleation and growth of 3 types of dislocation. These were the 60º glide dislocation, the 90º Lomer-Cottrell dislocation with stair-rod Shockley partials, and twinned wedge disclinations with 2-fold Σ = 9 coincidence boundaries between the wedge and matrix. It was suggested that, as the curvature at the root of a surface valley increased, the magnitude of the local elastic strain increased as a result of the local geometrical magnification of stress. The strain continued to increase in magnitude as the root sharpened, until the atomic ledges collapsed to form dislocations. Due to the resultant stress relief, subsequent mass transport reversed its direction of flow and caused dislocations to be trapped as bulk defects as the film surface moved away from the nucleation sites. It was concluded that, via this mechanism, dislocations could be nucleated without glide by surface trapping in films with even a modest level of nominal compressive mismatch strain.

Atomistic models of dislocation formation at crystal surface ledges in Si1-xGex/Si(100) heteroepitaxial thin films H.Gao, C.S.Ozkan, W.D.Nix, J.A.Zimmerman, L.B.Freund: Philosophical Magazine A, 1999, 79[2], 349-70