Molecular beam epitaxial growth of osmium silicides

Abstract

Details of the molecular beam epitaxial growth of osmium silicide (OsSi2 and Os2Si3) thin films are presented. The study has been motivated by reports that OsSi2 has a band gap between 1.4–1.8eV [L. Schellenberg et al., J. Less-Common Met. 144, 341 (1988); K. Mason and G. Muller-Vogt, J. Cryst. Growth 63, 34 (1983)], and Os2Si3 has a band gap of 0.95eV [A. B. Filonov et al., Phys. Rev. B 60, 16494 (1999)] or 2.3eV [L. Schellenberget al., J. Less-Common Met. 144, 341 (1988)]. Of particular note is that the Os2Si3 band gap is predicted to be direct, and thus has significant potential optoelectronic applications. The resulting films have been analyzed using reflection high-energy electron diffraction, scanning electron microscopy, x-ray reflectivity measurements, and out-of-plane x-ray diffraction. For low Si∕Os flux ratios (∼1.5), both OsSi2 and Os2Si3 phases are observed. However, with a larger Si∕Os flux ratio (∼4) the crystalline quality is greatly increased and only a single phase Os2Si3 is observed. We present our results and discuss our observations in relation to thermodynamic considerations and growth parameters.