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, d0, of ∼2.9–3.4nm showed a photoluminescence (PL) blueshift upon oxidatively induced size reduction, as expected from models of quantum confinement. Oxidation of smaller Si nanocrystals (d0∼2.5–2.8nm) also initially resulted in a PL blueshift, but a redshift in the PL was then observed after growth of ∼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.