Role of vacancy-type defects in the formation of silicon nanocrystals

The location and size distribution of silicon nanocrystals (Si-nc) formed in $SiO2$ by Si ion implantation and annealing were investigated. Transmission electron microscopy images revealed that the location and size distribution of the Si-nc are strongly correlated with the location of the vacancies produced in the $SiO2$ network by the implantation, as simulated by stopping and range of ions in matter and measured by positron annihilation spectroscopy (PAS). Simultaneous consideration of PAS and photoluminescence measurements suggest that the diffusion necessary for Ostwald ripening of Si-nc depends on the concentration and location of vacancy-type defects, and when the majority of these defects have been removed by annealing, the growth of the Si-nc slows dramatically or stops entirely. We demonstrate the capability for modification and enhancement of emission from Si-nc through the controlled introduction of defects into the oxide prior to annealing.