(Invited) Photo-Assisted Etching of Porous Silicon Nanostructures in Hydrofluoric Acid Using Monochromatic Light

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 A/min. The model was used to calculate porosity profiles during photoetching.