ELECTRONIC-STRUCTURE OF THIN SI LAYERS IN CAF2 - HYBRIDIZATION VERSUSCONFINEMENT

We present first principle calculations of thin (1-7 double layers) si licon (111) layers in CaF2, a system with strong analogies to porous s ilicon. We show that the Si band gap opening is dominated by the valen ce band which follows the effective mass confinement picture, while th e conduction band is found to flatten and shift very modestly due to h ybridization effects between Si and Ca states which lead to bonding-an tibonding interface states in the gap. The relevance of these results for Si-based low dimensional structures is discussed.