Size, shape, and crystallinity of luminescent structures in oxidized Si nanoclusters and H-passivated porous Si

摘要

Near-edge and extended x-ray absorption fine structure measurements from a wide variety of H-passivated porous Si samples and oxidized Si nanocrystals, combined with electron microscopy, ir-absorption, (alpha)-recoil, and luminescence emission data, provide a consistent structural picture of the species responsible for the luminescence observed in these systems. For luminescent porous Si samples peaking in the visible region, i. e., (le)700nm, their mass-weighted-average structures are determined here to be particles - not wires, whose short-range character is crystalline - not amorphous, and whose dimensions - typically <15 (angstrom) - are significantly smaller than previously reported or proposed. These results depend only on sample luminescence behavior, not on sample preparation details, and thus have general implications in describing the mechanism responsible for visible luminescence in porous silicon. New results are also presented which demonstrate that the observed luminescence is unrelated to either the photo-oxidized Si species in porous Si or the interfacial suboxide species in the Si nanocrystals.