A Gamma-ray Diffraction Study of MBE-Grown CaF2/Si(111) Heterostructures

MBE grown epitaxial films of CaF₂ onto Si(111) substrates were investigated by gamma ray diffraction to obtain assertions about the real structure and the strain situation in the epitaxial systems. It were measured the integral reflection coefficient R_i and the angle distribution of the reflected intensity of both (111) and (333) reflections. It was found that (i) a high temperature annealing step during the wafer preparation (1200 °C) causes a drastical increase of real structure defects in the substrate material, (ii) expitaxial layers of 18 nm thickness are grown pseudomorphically, layers having a thickness of 30 nm are relaxed, (iii) the misfit dislocation network formed during the relaxation process is localized not in the deposit but in the substrate material.