Results of the dielectric spectroscopy study of porous silicon (PS) samples in the frequency range, 20 Hz-1 MHz, and in the temperature range, 173-493 K, are presented. Three relaxation processes that dominate at low, moderate and high temperatures respectively were observed. The low temperature dispersion follows the Cole-Cole type with two activation energies of 0.28-0.4 and 0.2-0.3 eV for samples with thickness 20 and 30 μm, respectively. At moderate temperatures the time domain dielectric response function demonstrates stretch exponential behaviour associated with the percolation of charge carries near threshold. At temperatures above 400 K, we found a strong contribution of dc-conductivity, with approximately the same activation energy of 0.47 ± 0.01 eV for both samples. An additional Havriliak-Negami relaxation process with typical relaxation times of the order of 10-3 s is observed in this temperature interval. The dielectric response is found to be very sensitive to the geometrical micro- and meso-structural features of the PS. The dynamical aspects of the processes are discussed.
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The authors wish to thank Professors I. Balberg, J. Roisin and F. Kremer for helpful discussions. One of us (E.A.) acknowledges the Eshkol fellowship of the Israeli Ministry of Science, Culture and Sport for financial support.