Structural, chemical and optical characterisation of Ge-doped SiO2 glass films grown by magnetron rf-sputtering

Ge nanocrystals embedded in silicon dioxide (SiO2) films were prepared using the magnetron rf-sputtering technique. The films were characterised by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and optical transmission measurements. It was determined from X-ray diffractograms that the Ge particles have a diamond structure. The mean diameter of the nanocrystals was estimated to be between 30 and 80 Angstrom. XPS measurements showed that the Ge nanocrystals were very little oxidised. For the crystalline Ge particles, the size dependence of the Raman spectra of the TO phonon mode was observed. The increase in the line-width and the shift of the peak position to lower frequencies with decrease in their size are explained theoretically from quantum confinement effects of phonons. Optical transmission spectra clearly display a marked blue shift of the edge of the absorption band compared to bulk crystalline Ge, which is attributed to quantum size effects. (C) 1999 Elsevier Science S.A. All rights reserved.