Total external x-ray reflection and infrared spectroscopy study of porous silicon and its aging

Study of p-type porous silicon has been carried out by x-ray reflectometry for the first time. Its critical total-external-reflection angle and its reflection coefficient in the subcritical angle range are much smaller than for c-Si, which was grown by the Czochralski method. The critical angle decreases with increase of the porosity. The critical angle and the reflection coefficient increase with aging. These results are attributable to the much smaller electron density of porous silicon in comparison with c-Si, to the microgeometry of its surface, and to changes in both of these factors attendant to aging due to an increase in the concentration of atmospheric constituents observed in the infrared absorption spectra. As the porosity increases, the concentration of atmosmopheric impurities also increases, and in high-porosity material in addition to chemically adsorbed oxygen, carbon and water seem to contribute appreciably.