Structural properties of Ge nano-crystals embedded in SiO₂ films from X-ray diffraction and Raman spectroscopy

SiO₂ films containing small particles of Ge were grown using the r.f.-magnetron sputtering technique. The films were studied by means of X-ray diffraction (XRD) and Raman spectroscopy. XRD studies revealed diamond structure of Ge particles in the films grown at temperatures higher than 500°C. The dependence of the average size of Ge nanocrystals, determined by fitting the X-ray spectra (13-63 Å), on the substrate temperature, r.f.-power and the fraction of semiconductor in the target was determined. For higher-temperature grown films containing crystalline Ge particles, a pronounced peak due to confined optical phonons was observed in Raman spectra, while for those grown at lower temperature, there is just a broad band seen below 300 cm^-1. A theoretical model is applied to describe the contribution of optical phonons confined in small Ge spheres. © 1998 Elsevier Science S.A. All rights reserved.