Misfit dislocation generation in epitaxial layers

The misfit between an epilayer and a substrate may be accommodated either by misfit strain or by misfit dislocations, or by both jointly. For an epitaxial monolayer (ML) a critical misfit, depending primarily on bonding, exists below which it is stable when in registry with the substrate. When growth continues with the formation of a multilayer, misfit dislocations will enter at some critical thickness. The main objectives of this article are to critically review theoretical work aimed at explaining (1) the conditions under which an epilayer will grow in a ML-by-ML fashion to yield a uniform film and (2) the reasons why observed critical thicknesses and residual strains are often significantly in excess of the predicted ones, in terms of equilibrium and non-equilibrium concepts. Both (1) and (2) are of great fundamental and technological interest.