Optical and structural properties of encapsulated Si nanocrystals formed in SiO2 by ion implantation

A possible mechanism for the photoemission from Si nanocrystals in an amorphous SiO2 matrix fabricated by ion implantation is reported. We have measured the implantation dose dependence on the photoluminescence behavior images of Si nanocrystals in SiO2 layers, fabricated by ion implantation and a subsequent annealing step. After annealing, a photoluminescence band, peaking just below 1.7 eV, was observed. The peak energy of the photoluminescence was found to be affected by the dose of implanted Si ions, but to be independent of annealing time. We also present experimental results of high-resolution transmission electron microscopy (HRTEM) for each annealing step. The size of Si nanocrystals increases with increasing ion dose and annealing time. These results indicate that whilst the excitation photons are absorbed by Si nanocrystals, the emission is not simply due to electron–hole recombination inside the Si nanocrystals, but is related to the presence of some kind of defects, most likely located at the interface between the Si nanocrystals and the SiO2, for which the characteristic energy levels are affected by cluster–cluster interactions.