Mechanism for the formation of 90° dislocations in high-mismatch (100) semiconductor strained-layer systems

A rigorous calculation, within the framework of linear continuum elasticity, is performed to evaluate the energy of a rectangular 1/2[101](1̄11) 60° dislocation glide loop nucleated at the site of a pre-existing 1/2[1̄10](111) 60° dislocation at the (100) interface between a strained epitaxial layer and its substrate. This nucleation event gives rise to an interfacial segment of 1/2[011](100) 90° dislocation, which extends as the glide loop expands. The presence of the pre-existing 60° dislocation is found to reduce dramatically the energy of the loop relative to the energy of a comparable isolated loop. Results obtained for the elastic energy barrier to formation of such a loop for varying mismatch strain are incorporated into kinetic rate equations available in the literature. It is thus demonstrated that the mechanism of 90° dislocation formation described is expected to become experimentally significant at mismatch strains of around 2%. This result is in excellent agreement with the experimentally determined mismatch strain threshold at which significant 90° dislocation formation is observed to commence in GexSi1−x/Si(100) and InxGa1−xAs/GaAs(100) strained-layer heterosystems.