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 thr r.f.-magne tron sputtering technique. The films were studied by means of X-ray diffrac tion (XRD) and Raman spectroscopy. XRD studies revealed diamond structure o f Ge particles in the films grown at temperatures higher than 500 degrees C , The dependence of the average size of Ge nanocrystals, determined by fitt ing the X-ray spectra (13-63 Angstrom), on the substrate temperature, r.f.- power and the fraction of semiconductor in the target was determined. For h igher-temperature grown films containing crystalline Ge particles, a pronou nced peak due to confined optical phonons was observed in Raman spectra, wh ile for those grown at lower temperature, there is just a broad band seen b elow 300 cm(-1). A theoretical model is applied to describe the contributio n of optical phonons confined in small Ge spheres. (C) 1998 Elsevier Scienc e S.A. All rights reserved.