Contrasting photovoltaic response and photoluminescence for distinct porous silicon pore structures

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Abstract
The photoluminescent (PL) emission and photovoltaic (PV) response of two distinctly structured (prepared) porous silicon (PS) surfaces are compared and contrasted. The PV response of a porous silicon structure consisting of a microporous framework on which is superimposed a nanoporous layer is distinct from that of the branched nanoporous silicon structure generated in an aqueous etch environment. The observed PV response for this hybrid morphology is clearly not dominated by the covering nanoporous structure and displays a response that appears to be intermediate between those observed for nanoporous PS (band gap 1.80±0.2 eV) and crystalline silicon. In contrast, time-dependent histograms of the PL emission from the hybrid microporous-nanoporous and nanoporous structures, although not precisely the same, are quite similar. These observations, while consistent with a surface-dominated emission process associated with a bound fluorophor and not with the quantum confinement model, do suggest the influence of the PS bulk morphology on surface transformation.