Almost perfect epitaxial multilayers

Multilayers composed of many pairs of GaAs and Ga(As0.5P0.5) layers have been grown epitaxially on substrates whose lattice parameter matched that of the multilayer taken as a whole. The thickness of the individual layers in the multilayer was such that it was not energetically favorable for misfit dislocations to be made. Examination of thinned portions of these samples in a transmission electron microscope operating at 200 kV revealed that they were almost dislocation-free. They contained a few long dislocations that were present to accommodate part of the imperfect matching of the multilayer to its substrate. Images of these long dislocations were used to determine the planarity of interfaces between layers. It was found that the interfaces were flat to within the accuracy of measurement.