Dislocation migration across coherent phase interfaces in SiGe superlattices

Abstract

In this work we present a molecular dynamics study of a symmetrically strained SiGe superlattice subjected to compression. We measure the velocity of a dislocation nucleated at a step in the superlattice on a slip system that cuts across the interfaces, and compare it with that in single crystal Si and Ge for the same geometry. Simulation results of this work show that the phase interfaces in the short-period SiGe superlattice are free of misfit dislocations and that the average dislocation velocity in the SiGe superlattice sample is about two orders of magnitude lower than that in the Si and Ge single crystals for the same geometry and size. The effect of the coherent phase interfaces on the average dislocation velocity is quantified, and the underlying mechanism is identified. This work demonstrates that the coherency stress plays a dominant role on dislocation migration in coherent SiGe superlattices. It shows that a phase interface can impede or assist the migration of a dislocation depending on whether the sign of the stress field along the interface opposes or reinforces that of the dislocation core.