Role of the interface region on the optoelectronic properties of silicon nanocrystals embedded inSiO2

Light-emitting silicon nanocrystals embedded in ${\mathrm{SiO}}_2$ have been investigated by x-ray absorption measurements in total electron and photoluminescence yields, by energy filtered transmission electron microscopy and by ab initio total energy calculations. Both experimental and theoretical results show that the interface between the silicon nanocrystals and the surrounding ${\mathrm{SiO}}_2$ is not sharp: an intermediate region of amorphous nature and variable composition links the crystalline Si with the amorphous stoichiometric ${\mathrm{SiO}}_2.$ This region plays an active role in the light-emission process.