MOLECULAR-BEAM EPITAXIAL-GROWTH OF LOW-DIMENSIONAL SILICON STRUCTURESEMBEDDED IN CAF2

We report on the elaboration by molecular beam epitaxy of low dimensio nal silicon structures embedded in calcium fluoride, We have succeeded in fabricating nanocrystalline Si/CaF2 multilayers which exhibit effi cient visible luminescence at room temperature. The disappearance of t he luminescence when the Si layers become too thick, and the blue-shif t of the spectra when the Si layer thickness decreases, are consistent with a model based on quantum size effects. The important role of oxy gen as passivating agent after ageing in air, is also pointed out. We also present preliminary results on the growth of Si on CaF2 V-grooved films deposited on Si(110) substrates. Si nucleates along the [(1) ov er bar 10] direction and leads to islanding owing to the difference in surface free energy. (C) 1997 Elsevier Science S.A.