Epitaxial growth on silicon and characterization of MnF2 and ZnF2 layers with metastable orthorhombic structure

Abstract

The growth of MnF2 and ZnF2 layers on Si(001) and Si(111) substrates was studied by molecular-beam epitaxy. Calcium fluoride buffer layers with (001), (110), and (111) orientations were used to prevent chemical interaction of MnF2 and ZnF2 molecules with the Si substrate. The analysis of x-ray and reflection high-energy electron-diffraction (RHEED) patterns showed that MnF2 layers grow on all of these planes in the orthorhombic α-PbO2-type crystal phase observed earlier only at high pressures and temperatures. Atomic force microscopy revealed a strong dependence of the surface morphology on the buffer orientation and growth temperature. The best-ordered MnF2 growth occurred at 500 °C on a CaF2 (110) buffer layer. The diffraction analysis enabled us to find the epitaxial relations at the MnF2∕CaF2 interface. A careful analysis of the RHEED patterns of the films grown on CaF2(001) showed a similarity in the structure and growth modes between MnF2 and ZnF2 layers, with ZnF2 tending to form multiphase layers. These findings are in agreement with the x-ray diffraction measurements.