MECHANISM FOR THE FORMATION OF 90-DEGREES 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](111BAR) 60-degrees dislocation glide loop nucleated at the site of a pre-existing 1/2[110BAR](111) 60-degrees 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-degrees dislocation, which extends as the glide loop expands. The presence of the pre-existing 60-degrees 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-degrees 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-degrees dislocation formation is observed to commence in GexSi1-x/Si(100) and InxGa1-xAs/GaAs(100) strained-layer heterosystems.