On the use of low energy misfit dislocation structures to filter threading dislocations in epitaxial heterostructures

Abstract

Epitaxial deposits that consist of a substrate and a superlattice with layers alternating between positive and negative misfit are effective at reducing the density of threading dislocations. The superlattice is grown so as to minimize the number of dislocations which thread through the superlattice to the growth surface, i.e., to filter threading dislocations. The thickness of each superlattice layer exceeds a critical thickness for bending threading dislocations into a network of interfacial dislocations accompanied by mutual annihilation of the threading segments of the dislocations. This annihilation process takes place at a finite rate and benefits from annealing each layer of the superlattice before the next layer is grown. The thickness, annealing temperature and time are determined by the misfit between substrate and superlattice, and frictional forces on the dislocations. This process occurs primarily by glide but can also occur by climb. Once the number density of threading dislocations is sufficiently small that the probability of mutual annihilation is practically negligible, then another type of superlattice can be used to further filter the remaining dislocations. This second filter is one of layers whose misfits with the underlying layer are of the same sign. Equations are developed to describe the dislocation filter.