Microsc. Microanal. Microstruct. 8, 229-238 (1997)
DOI: 10.1051/mmm:1997119

Some Aspects of Coherent Epitaxial Deposits

Pierre Müller et Raymond Kern

Centre de Recherche sur les Mécanismes de la Croissance Cristalline , Campus de Luminy, case 913, 13288 Marseille Cedex 9, France

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 z₀. 2) Such layers accumulate strain energy and then may relax plastically by interfacial dislocations at a critical thickness z. 3) At some other critical thickness z, ( ), the monolayer growth becomes less stable than layer thickening, what leads to three-dimensional (3D) islanding on the z 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 . 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.

PACS
6855 - Thin film growth, structure, and epitaxy.
6810E - Fluid interface elasticity, viscosity, and viscoelasticity.
6150J - Crystal morphology and orientation.
6840 - Surface energy of solids: thermodynamic properties.
6810C - Fluid surface energy surface tension, interface tension, angle of contact, etc..
6240 - Anelasticity, internal friction and mechanical resonances.
6170G - Dislocations: theory.
6860 - Physical properties of thin films, nonelectronic.
6845B - Sorption equilibrium at solid fluid interfaces.

Key words
crystal morphology -- dislocations -- epitaxial growth -- epitaxial layers -- internal stresses -- island structure -- stress relaxation -- surface energy -- wetting -- coherent epitaxial deposits -- wetting -- thick planar substrate -- continuous pseudomorphous layers -- misfit strain -- accumulated strain energy density -- undersaturation -- plastic relaxation -- interfacial dislocations -- critical thickness -- monolayer growth -- layer thickening -- 3D islanding -- Stranski Krastanov growth -- lateral relaxation -- equilibrium shape ratio -- elastic energy -- equilibrium shape


© EDP Sciences 1997