Equilibrium Structure of a Thin Epitaxial Film

The dependence of the equilibrium configurations of a thin single‐crystalline epitaxial film, on the strengths of substrate‐overgrowth and overgrowth‐overgrowth bonds and the interfacial misfit is calculated neglecting substrate deformations. Previous analyses of the system were based on a one‐dimensional model, allowing for misfit, i.e., differing lattice parameters, in one interfacial direction only. The results of these analyses show (i) that interfacial mismatch is accommodated by a parallel sequence of misfit dislocations, (ii) that the mismatch decreases when appropriate overall lateral strains are introduced, (iii) that in stable and metastable film configurations both dislocations and overall strains are present, and (iv) that there exist limiting misfits 2/πl0 and 1/l0, respectively, below which the stable and metastable states are pseudomorphic; the film is homogeneously strained to coherency, i.e., exact fit, with the substrate. The transition to the noncoherent state is critical, the change in...