Raman spectroscopy of Si-rich SiO2 films: Possibility of Si cluster formation

Si-rich SiO2 films were prepared by a RF cosputtering method and their Raman, infrared absorption and photoluminescence (PL) spectra were measured as functions of Si concentration and annealing temperature. The Raman spectrum was found to change depending on the Si concentration and annealing temperature and differ from those of well known various types of Si. Characteristic features of the spectra are in good qualitative agreement with the theoretical results of a phonon density of states in Si clusters (Si-33 and Si-45) calculated by Feldman et al. The present Raman spectra are thus concluded to arise from the Si clusters formed in the films. The spectral changes depending on the excess Si concentration and annealing temperature can be explained in terms of the change in the average size of the clusters. The films also exhibited PL in the visible region. Good correlation between the Raman and PL spectra leads us to conclude that the PL arises from the Si clusters in the films.