AC impedance spectroscopy of porous silicon thin films containing metallic cations

Thin porous silicon (PS) films were prepared by HF/HNO3 vapor etching on silicon wafers. The infiltration of metallic cations inside the porous silicon matrix followed by slow heating in air leads to an interesting electrical and optical physical phenomena. Al3+, Cu+, K+, Li+ metallic cations as chloride or as nitrate solutions are infiltrated inside the silicon porous matrix. After annealing in air at 500 °C during 2 h a structure was achieved in order to measure the Nyquist diagram corresponding to the cations embedded in PS/silicon. The real and imaginary parts of the whole structure depend on the voltage bias and on the frequency. Those signify that the junction is a Schotky-barrier junction.From the variation of Ln(σT) versus absolute temperature T, where σ is the conductivity, we have deduced the activation energy of the metallic impurities in the [100 °C–400 °C] temperature range. We have found that the activation energies are of about 0.19 eV, 0.25 eV, 0.49 eV and 0.71 eV for Cu+, K+, Al3+ and Li+ cations respectively. These kinds of structures are suitable for gas sensing, optical sensing or for the fabrication of fuel cell membranes.