Room temperature photoluminescence from amorphous silicon nanoparticles in SiOx thin films

Amorphous SiOx thin films with four different oxygen contents (x=1.15, 1.4, 1.5, and 1.7) have been prepared by thermal evaporation of SiO in vacuum and then annealed at 770 or 970 K in argon for various times ⩾40 min. The influence of annealing conditions and the initial film composition on photoluminescence (PL) from the annealed films has been explored. Intense room temperature PL has been observed from films with x⩾1.5, visible with a naked eye. It has been shown that PL spectra of most samples consists of two main bands: (i) a 'green' band centered at about 2.3 eV, whose position does not change with annealing conditions and (ii) an 'orange-red' band whose maximum moves from 2.1 to 1.7 eV with increasing annealing time and temperature and decreasing initial oxygen content. These observations have been explained assuming recombination via defect states in the SiOx matrix for the first band and emission from amorphous Si nanoparticles for the second one.