Formation of luminescent Si nanocrystals by high-temperature annealing of ion-beam-sputtered Si/SiO₂ multilayers

Si/SiO₂ multilayers (MLs) have been prepared under different deposition temperatures (T_S) by ion beam sputtering. The annealing at 1200°C leads to the formation of Si nanocrystals in the Si layer of MLs. The high resolution transmission electron microscopy images clearly demonstrate the existence of Si nanocrystals, which exhibit photoluminescence (PL) in the visible range when T_S is ≥ 300°C. This is attributed to well-separation of nanocrystals in the higher-T_S samples, which is thought to be a major cause for reducing non-radiative recombination in the interface between Si nanocrystal and surface oxide. The visible PL spectra are enhanced in its intensity and are shifted to higher energy by increasing T_S. These PL behaviours are consistent with the quantum confinement effect of Si nanocrystals.