It was recalled that, during the hetero-epitaxial growth of films having large misfits with respect to the underlying substrate, the generation of misfit dislocations and threading dislocations was widespread at thicknesses which were much greater than the equilibrium critical thickness. Experimental data suggested that, after entanglement in a region near to the film/substrate interface, there was a fall-off in threading dislocation density that was inversely proportional to the film thickness. This was true for densities which ranged from 107 to 109/cm2, and was followed by saturation or weak decay of the threading dislocation density with further increases in film thickness. The present work was based upon a recent framework for understanding threading dislocation reduction in terms of their effective lateral motion with increasing film thickness; coupled with the probability that certain pairs of threading dislocations annihilated to form a single threading dislocation, or underwent a change in line direction. A computer simulation approach was used which improved upon a recent theoretical prediction of an inverse thickness dependence and of a saturation of threading dislocation densities. Specific cases were considered which involved threading dislocation distributions that were typical of surface nucleation, island periphery nucleation and various combinations. Results were presented which suggested that long-range fluctuations in the net Burgers vector content of the local threading dislocations were the cause of a saturation behaviour.

Computer Simulation of Threading Dislocation Density Reduction in Heteroepitaxial Layers. G.E.Beltz, M.Chang, J.S.Speck, W.Pompe, A.E.Romanov: Philosophical Magazine A, 1997, 76[4], 807-35