Substrate Step Induced Strain in Heteroepitaxial Growth

Abstract

During epitaxial growth of lattice-mismatched materials, substrate surface steps induce vertical misfit between substrate and epilayer. It is shown that the resulting strain is accomodated by an interface dislocation, which is of the Read-Shockley type for a complete step and supplemetary displacement type for a demistep, using R.C. Pond’s classification. Alternative models for the strain accomodation are considered. A localized “displacement boundary” is shown to be unfavorable irrespective of the film-thickness. Residual shear strain in the film requires debonding from the substrate, which is shown to be unfavorable with respect to the dislocation model. The distribution of strain between film and substrate is shown to depend weakly on film-thickness but strongly on the material’s elastic constants.