Effect of passivation and aging on the photoluminescence of silicon nanocrystals

Silicon nanocrystals were prepared by laser pyrolysis of silane in a gas flow reactor and deposited on substrates by cluster beam deposition. The evolution of the photoluminescence was measured as a function of the time the samples were exposed to air. With gradual air exposure and oxidation, the photoluminescence increases in intensity and its peak wavelength shifts to the blue. At the same time, the photoluminescence band becomes wider. To remove the oxide layer, the samples were exposed to hydrofluoric acid (HF) vapor. The HF attack has no influence on the band position but leads to a smaller width. The observations can be explained in terms of quantum confinement as the origin of the photoluminescence. Only for the smallest Si nanocrystals, an interface state seems to limit the maximum photoluminescence energy to 2.1 eV.