The progress of the chemical dissolution of porous silicon (PSi) formed from lightly-doped p-type silicon in ethanoic HF solutions was monitored by recording in situ the photocurrent from monochromatic illuminations, which was used as a measure of optical transmission. The relations between dissolution time, porosity, and absorption coefficient were established and the porosity-dependence of the absorption coefficient derived from ∼60% porosity to 100% porosity. The absorption results were discussed considering the Bruggeman model of effective medium approximation and other measurements from the literature, together with the effects of quantum confinement (QC) and surface states. The porosity and spectral dependences of the QC in the absorption spectra were clearly observed. QC in the blue spectral range (<500 nm) was found to require extremely high porosities (>85%), contrary to the red to green region, where QC was identified for the whole porosity range studied. Our procedure allows the continuous exploration of a wide range of porosities, without limitation on the high side, while preserving an ideal hydrogen-terminated PSi surface and very good structural integrity, as PSi is always kept in HF solution and never dried. The study also allows the determination of the dissolution rate of silicon in various HF-based solutions.

No abstract

Photo-assisted etching of porous silicon (PSi) in hydrofluoric acid (HF) solution has been, so far, not well controlled and characterized. In this paper, the progress of photoetching of PSi formed from lightly-doped p-type silicon in ethanolic HF solutions was monitored using an in situ photoconduction technique. A model was proposed to explain the results. Two regimes were characterized, one in which the photoetch rate is limited by the supply of photo-generated holes at the Si surface, and another one where it is limited by the rate R 0 of the chemical reactions after initial hole capture, for illumination powers greater than a threshold value. This value was about 1 mW/cm 2 when using a wavelength of 450 nm for a porosity of 62%. R 0 was evaluated as about 0.06 Å/min. The model was used to calculate porosity profiles during photoetching. The effect of illumination wavelengths is discussed. A signature of quantum confinement in high-porosity PSi was observed.

No abstract

Photo-assisted etching of porous silicon (PSi) in hydrofluoric acid (HF) solution has been, so far, not well controlled and characterized. In this paper, the progress of the photoetching of PSi formed from lightly-doped p-type silicon in ethanoic HF solutions was monitored using an in situ photoconduction technique. A model was proposed to explain the results. Two regimes were characterized, one in which the photoetch rate is limited by the supply of photo-generated holes at the Si surface, and another one where it is limited by the rate R0 of the chemical reactions after initial hole capture, for illumination powers greater than a threshold value. This value was about 1 mW/cm2 when using a wavelength of 450 nm for a porosity of 62%. R0 was evaluated as about 0.06 Å/min. The model was used to calculate porosity profiles during photoetching.