Defect-related versus excitonic visible light emission from ion beam synthesized Si nanocrystals in SiO2

Two sources of room temperature visible luminescence are identified from SiO₂ films containing ion beam synthesized Si nanocrystals. From a comparison of luminescence spectra and photoluminescence decay lifetime measurements between Xe⁺-implanted SiO₂ films and SiO₂ films containing Si nanocrystals, a luminescence feature attributable to defects in the SiO₂ matrix is unambiguously identified. Hydrogen passivation of the films selectively quenches the matrix defect luminescence, after which luminescence attributable to Si nanocrystals is evident, with a lifetime on the order of milliseconds. The peak energy of the remaining luminescence attributable to Si nanocrystals 'redshifts' as a function of different processing parameters that might lead to increased nanocrystal size and the intensity is directly correlated to the formation of Si nanocrystals. Upon further annealing hydrogen-passivated samples at low temperatures (<500 °C), the intensity of nanocrystal luminescence increases by more than a factor of 10.