Electroluminescence from silicon nanocrystals in Si/CaF2 superlattices

Electroluminescence (EL) from silicon nanocrystals in Si/CaF2 superlattices grown by molecular-beam epitaxy at room temperature was investigated and compared with that obtained from silicon nanocrystals in Si/SiO2 superlattices. EL spectra exhibited current-tunability, similar to that observed in silicon nanocrystals in SiO2, which was attributed to three main effects: (a) Auger quenching of photoluminescence, which occurs when more than one electron-hole pair is present in the same nanocrystal and which quenches luminescence from relatively larger nanocrystals, (b) size-dependent carrier injection, and (c) the effect of the applied field, when this one is significantly high. In the case of Si/CaF2 superlattices, this last factor did not apply, so the two other factors are mainly at the origin of the effect.