光音響分光法によるポーラスシリコンの評価

概要

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We are interested in an investigation of porous silicon by means of photoacoustic spectroscopy. This spectroscopic method has the characteristic that the absorption of a material can be estimated even when the other material exists on the backside. The feature of the method is applicable to porous silicon that is usually formed on a silicon substrate. The amplitude of photoacoustic spectra has been discussed so far, but not the phase of the spectra. We have grown porous silicon on silicon single crystals by anodization for three different kinds of anodization time and investigated the variation of the phase with respect to the chopping frequency. The dependence of the phase on incident photon energy, which is not quite different from that of amplitude, does not give any additional information. On the other hand, the dependence on chopping frequency was found to be quite different from that of the amplitude. We also found that the inclination of the phase signal with respect to the logarithm of chopping frequency is dependent on the anodization time when the incident photon energy is in the region where the photon is absorbed at the surface of the porous layer.