Lattice and thermal misfit dislocations in epitaxial CaF2/Si(111) and BaF2-CaF2/Si(111) structures

Abstract

Atomic force microscopy reveals straight slip steps resulting from dislocation glide in the primary {100}〈110〉 glide system in ‘‘low mismatch’’ ${\mathrm{CaF}}_2$/Si(111) structures. From the height and spacing of the steps, the strain relieved by these misfit dislocations is compatible with the relief of the tensile thermal strain change on cooldown. In ‘‘high mismatch’’ ${\mathrm{BaF}}_2$/${\mathrm{CaF}}_2$/Si(111) structures, dislocations which relieve the thermal mismatch change are mobile, while the 14% lattice mismatch is mainly overcome by sessile misfit dislocations with Burgers vectors parallel to the interface.