Size-dependent oxygen-related electronic states in silicon nanocrystals

Silicon nanocrystals embedded in SiO2 were isolated with a selective etching procedure, and the isolated nanocrystals' excitonic emission energy was studied during controlled oxidation. Nanocrystals having initial diameters, d(0), of similar to 2.9-3.4 nm showed a photoluminescence (PL) blueshift upon oxidatively induced size reduction, as expected from models of quantum confinement. Oxidation of smaller Si nanocrystals (d(0)similar to 2.5-2.8 nm) also initially resulted in a PL blueshift, but a redshift in the PL was then observed after growth of similar to 0.3 monolayers of native oxide. This decrease in excitonic emission energy during oxidation is consistent with the theoretically predicted formation of an oxygen-related excitonic recombination state