Properties of lattice mismatched IIa-fluorides on silicon

Abstract

Films of BaF 2 have been grown by molecular beam epitaxy on Si(100) and Si(111) which was covered with thin CaF 2 and/or SrF 2 to obtain perfect epitaxy. The BaF 2 (100) layers grown on SrF 2 /Si(100) using a two-temperature method do not show (111)-facetted surfaces, but smooth BaF 2 (100) surfaces can be obtained despite the high lattice mismatch and preferred (111) growth mode. This indicates that the large free (100)-surface energy of fluorides reduces to a value below 3 1 2 times that of the (111) surface at high growth temperatures. The depth distribution of strains in (111)-oriented stacks has been determined by Rutherford backscattering channelling angular scans. The thermal mismatch strain relaxation leads to a small residual strain across the BaF 2 layers, while steps in the magnitude of the strains occur at fluoride-fluoride and silicon-fluoride interfaces. The layers are intended as epitaxial buffers for heteroepitaxy of lattice and thermal expansion mismatched II–VI and IV–VI compound semiconductors on silicon.