Optical properties of Si/CaF2 superlattices

We present a first-principle theoretical study of the dielectric functions of Si/CaF2 superlattices. In particular, we investigate how the optical response depends on the thickness of the Si layers. Our results show that for very thin Si slabs (well width less than ~20 \uc5) optical excitation peaks are present in the visible range. These peaks are related to strong transitions between localized states. Moreover, the static dielectric costant is considerably reduced. From the comparison made with recent experimental data on similar systems we conclude that the quantum confinement, a good surface passivation and the presence of localized states are the key ingredients in order to have photoluminescence in confined silicon based systems