SOME ASPECTS OF COHERENT EPITAXIAL DEPOSITS

When wetting is complete, coherent epitaxies on a thick planer substra te B build up z continuous pseudomorphous layers A which are fully str ained according to their natural misfit m. The so-accumulated strain e nergy density is responsible for some remarkable facts: 1) Each layer is formed at precise undersaturation. At saturation there is a specifi c number of wetting layers z(0). 2) Such layers accumulate strain ener gy and then may relax plastically by interfacial dislocations at a cri tical thickness z(d1). 3) At some other critical thickness z(SK), (z(0 ) < Z(SK) < Z(d1)): the monolayer growth becomes less stable than laye r thickening, what leads to three-dimensional (3D) islanding on the z( sk) wetting layers, called Stranski-Krastanov (SK) growth. Such island s laterally relax and, since coherent with their substrate, drag the s ubstrate 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 not equal C)) and relaxed crystal, the strain opposes to wetting, s o that the higher the elastic energy, the greater tile shape ratio r(m ). 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.