Light Emission from Porous Silicon Photoetched in Aqueous Alkali Salt Solutions

Abstract

An interband-transition model was applied to explain the emission mechanism in porous silicon (PSi) fabricated by photoetching in aqueous HF and salt (NaF and KF) solutions. The HF-formed samples show a yellow photoluminescence band at ∼2 eV. The salt-formed samples, on the other hand, show an ultraviolet (UV) emission peak at ∼3.3 eV with a spectral width of ∼0.1 eV, together with a broad emission band at ∼2.7 eV. The broad emission bands at ∼2 and ∼2.7 eV can be explained by the quantum-mechanical confinement effect, i.e., a relaxation of the momentum conservation at and above the indirect-absorption edge (supra-EgID emission). This effect may also lead to a change in the E1 critical point (CP) from the two-dimensional M0 to the zero-dimensional CP with decreasing nanocrystalline size. The change in the E1-CP dimensionality makes possible an emission in the UV region with a narrow spectral width.