ELECTRONIC-STRUCTURE OF THIN SI LAYERS IN CAF2 - HYBRIDIZATION VERSUS CONFINEMENT

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