Some aspects of coherent epitaxial deposits

Abstract

When wetting is complete, coherent epitaxies on a thick planar substrate B build up z continuous pseudomorphous layers A which are fully strained according to their natural misfit m. The so-accumulated strain energy density is responsible for some remarkable facts: 1) Each layer is formed at precise undersaturation. At saturation there is a specific number of wetting layers ZQ. 2) Such layers accumulate strain energy and then may relax plastically by interfacial dislocations at a critical thickness z < ZSK < Zdi), the monolayer growth becomes less stable than layer thickening, what leads to three-dimensional (3D) islanding on the zsk wetting layers, called Stranski-Krastanov (SK) growth. Such islands laterally relax and, since coherent with their substrate, drag the substrate which relaxes too. 4) If the equilibrium shape ratio r of non misfitted 3D deposit (m = 0) depends on the wetting, for a misfitted (m 0) and relaxed crystal, the strain opposes to wetting, so that the higher the elastic energy, the greater the shape ratio rm. 5) Since the equilibrium shape of a 3D crystal depends upon strain, at each dislocation entrance the shape ratio of the crystal varies in a sudden way. © EDP Sciences 1998.