The mechanism of light emission from porous silicon: where are we 7 years on?

This paper aims to offer a judgement on the origin of the efficient visible photoluminescence (PL) from porous silicon in light of the mass of evidence now available 7 years after Canhamʹs initial work. The introductory section provides a brief history of porous silicon and outlines the quantum confinement model of the luminescence. The following section presents the alternative models under five groupings. In the results section a wide range of evidence relevant to the origin of the luminescence is discussed in general terms, following which the results of three spectroscopic studies are discussed in detail. These deal with the splitting of the luminescent states in porous silicon, the polarisation of the luminescence and the phonon replicas seen in PL spectra under resonant excitation. The weight of this evidence is shown to demonstrate that the quantum confinement model of the luminescence is correct, and additionally that carrier localisation on the atomic scale is inconsistent with the experimental results.