Band gap of porous silicon

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Abstract
We observe a quadratic rise of the absorption coefficient with excitation energy in photoluminescence excitation spectra of porous silicon. Extrapolation to α=0 yields an average band gap of microporous silicon about 0.2 eV above the luminescence line. Good agreement is obtained with an estimate of the band gap from the position of the second luminescence line of porous silicon in the infrared spectral region. Further analysis of the line shape using different luminescence detection energies show that, in addition to the size distribution of crystallites, there exists a second contribution to the linewidth.