CHARACTERIZATION OF THIN EPITAXIAL CAF2 LAYERS ON SI(111) USING IMPURITY LUMINESCENT PROBES, X-RAY STANDING WAVES AND X-RAY-DIFFRACTOMETRY

The structure, crystalline quality and elastic strain of CaF2 epitaxial layers on Si(111) substrates have been studied using an impurity photoluminescent probe, x-ray standing waves and x-ray rocking curves. Molecular beam epitaxy was used to grow 10 nm thick films. The CaF2/Si(111) interface was formed at 770-degrees-C and the films were grown at temperatures of 100, 550, 660 and 770-degrees-C. There is good agreement between the elastic strain values measured from the low-temperature photoluminescence spectra of Sm2+ ions and x-ray rocking curves. It is confirmed that films grown below 550-degrees-C are pseudomorphic, and the relaxation of lattice mismatch stress occurs at higher temperatures. Analysis of the angular dependence of x-ray Ca fluorescence under the x-ray standing wave conditions has shown the distance between the Ca and Si crystallographic planes adjacent to the interface to be 2.89 +/- 0.03 angstrom, which corresponds to the dominant Ca-Si bonds at the interface.