Photoionization of silicon particles in SiO2

The density of electron states of nm-size Si particles in SiO2 layers produced by implanting O+ ions into Si is analyzed using a newly developed total optical depopulation technique. The distribution of states is found to be indistinguishable for neutral and negatively charged particles, and nearly independent of the particle size. This indicates that the optical excitation is related to defects in the oxide surrounding the particles. Two components of the defect spectrum are isolated, both related to the Si enrichment of the oxide, with energy levels at 2.8 and 3.1 eV below the SiO2 conduction band. The latter is related to the H-complexed O vacancy in SiO2 and its contribution is significantly enhanced upon hydrogenation. Electron states originating from quantum confinement in Si particles are observed only in the smallest Si clusters; in all other cases electrons are found to be trapped in the oxide. The blue luminescence, known for the oxidized Si particles, may be consistently explained from;the obtained electronic spectra suggesting the charge transfer between a Si particle and neighboring oxide defects as a feasible mechanism. [S0163-1829(99)06003-8].