MBE GROWTH OF SI CAF2 NANOSTRUCTURES - PHOTOLUMINESCENCE AND ABSORPTION PROPERTIES/

We have investigated the optical properties of nanocrystalline Si/CaF2 multilayers grown by molecular beam epitaxy. The optical absorption e dge shows a large blue shift for decreasing Si layer thickness while t he luminescence is slightly affected. This brings us to the conclusion that the luminescence is related to localized states far below the op tical absorption edge which is sensitive to quantum confinement effect s. These deep luminescent centers can be filled after the broadening o f the gap when the Si layer thickness becomes thin enough. We also pre sent preliminary results on the growth of Si on CaF2 V-grooved films d eposited on Si(110) substrates. Si nucleates along the [110] direction and leads to islanding due to the difference in surface free energy.