ON THE USE OF LOW-ENERGY MISFIT DISLOCATION-STRUCTURES TO FILTER THREADING DISLOCATIONS IN EPITAXIAL HETEROSTRUCTURES

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 i s grown so as to minimize the number of dislocations which thread thro ugh the superlattice to the growth surface, i.e., to filter threading dislocations. The thickness of each superlattice layer exceeds a criti cal thickness for bending threading dislocations into a network of int erfacial dislocations accompanied by mutual annihilation of the thread ing segments of the dislocations. This annihilation process takes plac e at a finite rate and benefits from annealing each layer of the super lattice before the next layer is grown. The thickness, annealing tempe rature and time are determined by the misfit between substrate and sup erlattice, and frictional forces on the dislocations. This process occ urs primarily by glide but can also occur by climb. Once the number de nsity of threading dislocations is sufficiently small that the probabi lity of mutual annihilation is practically negligible, then another ty pe of superlattice can be used to further filter the remaining disloca tions. This second filter is one of layers whose misfits with the unde rlying layer are of the same sign. Equations are developed to describe the dislocation filter.