Characterization of thin epitaxial CaF2 layers on Si(111) using impurity luminescent probes, X-ray standing waves and X-ray diffractometry

Abstract

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+or-0.03 AA, which corresponds to the dominant Ca-Si bonds at the interface.