Annealing effects on structures and optical properties of silicon nanostructured films prepared by pulsed-laser ablation in inert background gas

We studied the annealing effects on the structures and optical properties of silicon (Si) nanostructured films. The Si nanostructured films were synthesized by pulsed-laser ablation in inert background gas. It was found that the Si nanostructured films partially include an amorphous-like structure under the as-deposited condition. After annealing in nitrogen gas, the crystallinities of the Si nanoparticles recovered, and four visible photoluminescence (PL) bands (1.7, 2.2, 2.7, and 3.1 eV) appeared at room temperature. Furthermore, upon subsequent annealing in oxygen gas, strong quantum confinement effects for both phonons and carriers of the Si nanoparticles appeared, and the relative intensity of the 2.7 eV blue band increased. We fabricated electroluminescent (EL) diodes with active layers of annealed Si nanostructured films, and verified visible EL spectra at room temperature, which exhibited the same trends as the PL spectra. A possible explanation for the increase of relative intensity of the 2.7 eV blue band is the increase of the amount of silicon dioxide, which contains neutral oxygen vacancy defects, in the Si nanostructured films.