Quenching of Reducing Properties of Mesoporous Silicon and Its Use as Template for Metal/Semiconductor Deposition

Abstract

We report on a study of the formation of crystalline copper and nanocrystalline cuprous oxide at electrochemically prepared mesoporous silicon surfaces immersed in a copper sulfate solution. The metal deposition on porous silicon, either by using the reducing properties of the as-prepared native mesoporous surface (immersion plating) or by applying an external current (electroplating), is investigated by IR spectroscopy, X-ray diffraction, and scanning electron microscopy. The degree of oxidation and the surface chemistry of the porous epilayers (porosity 50%, mean pore diameter 10 nm, and pore length 25 μm) are varied by annealing at different temperatures. For immersion plating, we observe the formation of face-centered cubic copper crystals with irregular shapes and a broad size distribution from the nano- to the micrometer scale. Electroplating of as-prepared porous layers leads to a crystalline copper film which homogeneously covers the porous silicon surface. By contrast, electroplating of partially oxidized porous layers leads to isolated single copper crystals with quadratic bipyramidal shape at the outer porous epilayer surface and a sizable fraction of nanochannel confined crystalline , a prominent candidate for the investigation and application of quantum confinement effects in semiconductors.