DISLOCATIONS AND STRAIN RELIEF IN COMPOSITIONALLY GRADED LAYERS

The performance of strained-layer heterostructures is often limited by threading dislocations. Such defects can be reduced, and in some cases nearly eliminated, by growing a graded buffer layer. Here, we provide a quantitative picture of the role of grading, by calculating the equilibrium distribution of dislocations and residual strain in such compositionally graded films. In layers with graded strain, threading dislocations are subject to greater force and weaker pinning than in uniform layers, helping them to be swept to the edge of the sample.