Surface morphology of epitaxial CaF2 films on Si substrates

Abstract

The surfaces of epitaxial CaF2 layers grown on (100) and (111) Si by molecular beam epitaxy have been studied using scanning electron microscopy. The (111) surface exhibits small triangular hillocks, while the (100) surface exhibits a columnar structure. This latter structure can be accounted for by the prohibitively large free energy of the (100) surface. A dipole moment exists perpendicular to this surface which causes the electrostatic energy to diverge. This phenomenon explains the inferior (100) growth as compared to (111) and has important implications for possible applications of group II-A fluoride/semiconductor epitaxial structures.