Optical characterization of Si nanocrystals in Si-rich SiO _x and SiO _x/SiO ₂ multilayers grown by ion beam sputtering

Si-rich SiO _x single-layer and SiO _x/SiO ₂ multilayer (ML) films have been prepared by ion beam sputtering under various conditions of stoichiometry of the SiO _x layer and deposition temperature (T _S). Annealing at 1100°C leads to the formation of Si nanocrystals in the SiO _x layers. The phase separation between SiO ₂ matrix and Si hanocrystals is more clearly seen at higher T _S. High-resolution transmission electron microscopy images clearly demonstrate the existence of Si nanocrystals, which exhibit photoluminescence (PL) in the visible range. The PL intensity of the MLs decreases with increasing x or T _S, which turns out to be caused by the reduction of the nanocrystalline Si fraction, The PL spectra are blue-shifted by increasing the oxygen content (x) or decreasing the layer thickness, which is consistent with the quantum confinement effect.