Size dependence of the luminescence properties in Si nanocrystals

We have observed strong room temperature photoluminescence (PL) from high temperature annealed, substoichiometric silicon oxide (SiOx) thin films, prepared by plasma enhanced chemical vapor deposition. The PL peaks have been found in the 650–950 nm spectral range; peak intensities increase with the annealing temperature up to 1250°C. A marked redshift of the luminescence peaks has been observed by increasing the Si concentration of the SiOx films as well as the annealing temperature. Transmission electron microscopy analyses have demonstrated that Si nanocrystals (nc), having mean radius ranging between 0.7 and 2.1 nm, are present in the annealed samples, and that their size increases with increasing the Si content and the annealing temperature. Structural and optical data have been related and discussed in terms of quantum carrier confinement.