Photoluminescence mechanisms in silicon quantum dots embedded in nanometric chlorinated-silicon nitride films

Silicon quantum dots (Si-QDs) embedded in nanometric (∼80 nm) chlorinated-silicon nitride films (SiNx:Cl) were prepared by remote plasma enhanced chemical vapor deposition. The photoluminescence (PL) peak and the two optical absorption edges observed in the PL and absorption spectra of the films were tuned (blue-shifted) as the Si-QD size was decreased, giving evidence of quantum confinement effects. From these results we elucidate that the photoluminescence in these nanostructured films is generated by photoexcitation of electrons from the valence band tail of the SiNx:Cl matrix toward the conduction band tail of the SiNx:Cl matrix and the conduction band of the Si-QDs, followed by diffusion and transfer of electrons and holes from the SiNx:Cl matrix to the Si-QDs, and then electron–hole radiative recombination in the Si-QDs. These PL mechanisms explain quite well the large absorption/emission Stokes shift that was experimentally observed in these films.