Influence of water and alcohols on photoluminescence of porous silicon

The measurements of luminescence spectra were performed on series of porous silicon (PS) samples, obtained in wide range of anodic etching regimes. Photoluminescence (PL) spectra contain two closely spaced luminescence bands. The energy difference between them similar to 0.15-0.2 eV depends very slightly on their spectral position. The ratio of the intensities of the two PL bands is monotonously changing with the changes in sample porosity. Thus, in very porous samples only the short-wavelength band is usually observed, while in slightly porous samples only the long-wavelength band is observed. Interaction of PS samples with water at first produces a small decrease of PL band intensities, and then a new band in the range of 0.7 mu m appears, which is presumably related to an oxide layer at the surface of PS nanocrystallites. After treating PS in alcohols, the initial band intensity drops and the long-wavelength band disappears completely in less than 1 min. It is discovered that the presence of water contained in the ethanol (even at a content of similar to 1%), leads to emergence of a new intensive PL band in the range of 0.7 mu m. In very porous samples or after washing or storage of as-anodized PS in water or alcohols, the long-wavelength band is rarely observed experimentally because its intensity is very small. (C) 1996 American Institute of Physics.