Ultraviolet emission from porous silicon photosynthesized in aqueous alkali fluoride solutions

Abstract

Stable ultraviolet ͑UV͒ photoluminescence ͑PL͒ has been observed at room temperature in porous silicon ͑PSi͒ fabricated by photoetching in aqueous alkali fluoride solutions. The aqueous solutions used are 1 M NaF and 1 M KF. They give an alkaline reaction caused by partial hydrolysis. The PL peaks at ϳ3.3 eV have a full width at half maximum of ϳ0.1 eV, which is much smaller than those reported previously ͑ജ0.5 eV͒. Spectral analyses suggest that both quantum confinement and surface passivation effects enable the observation of UV emission in NaF-and KF-prepared PSi samples.

Light Emission from Porous Silicon Photoetched in Aqueous Alkali Salt Solutions

“…The PL spectra reported here are measured from our newly prepared PSi samples. These are essentially the same as those reported previously, 4,5) but the $2:7 eV emission intensity is stronger than those reported previously. An interband-transition model 6) is used to explain PL mechanisms in such photoetched PSi samples.…”

“…The PL spectrum for the HF-prepared PSi sample shown in Fig. 1(c) exhibits a very broad emission band peaking at $1:95 eV, 4,5) which is typically observed in PSi fabricated by anodic or stain etching in HF-based solutions. Photoetched PSi was first reported by Noguchi and Suemune, 10) who used 50% HF solution for etching and a He-Ne laser as the light illumination source and observed light emission at $1:85 eV ($675 nm).…”

“…In fact, our measured FTIR spectra suggested no presence of polysilane chains or films on the KF-and NaF-prepared samples. 4,5) Even if polysilane films were formed, it would be very difficult to expect efficient PL emission from such thin films.…”

“…Recently, we fabricated light-emitting PSi by photoetching in aqueous salt (NaF and KF) solutions. 4,5) Strong ultraviolet (UV) emission at $3:3 eV was observed with a very narrow full width at half maximum (FWHM) of $0:1 eV, together with a broad emission band at $2:7 eV. Although the surface oxide produced during/after photoetching is suggested to play an important role in the UV emission, the detailed emission mechanism is not clear at present.…”

Spectroscopic investigation of light-emitting porous silicon photoetched in aqueous HF∕I2 solution

“…As the PSi nanocrystalline size observed by atomic force microscopy ͑AFM͒ is of the order of 20Ϫ100 nm, 10,44 we adopt a concept of the Brillouin zone not only about c-Si but also about PSi. The corresponding energy-band structures and density-of-states spectra are schematically shown on the left-hand side of Fig.…”