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This paper considers a theoretical model of the metal-tunnel interface layer-thin porous silicon-p-Si structure. A diffusion-drift equation at the appropriate boundary conditions is solved to clarify a mechanism of the carriers' transport. The voltage drop distribution along the structure is calculated by solving the equations under the condition of continuity of the vector of the electrostatic induction. The obtained analytical expressions allow one to analyse the contribution of the interface layer, porous silicon and surface electron states to the electrical behaviour of the structure. Some parameters of the model are defined from the comparison of experimental I-V and C-V characteristics with theoretical values for the Pd-porous silicon (60% of porosity)-p-Si structures having different thicknesses of porous silicon layers. The defined barrier height eφ0 ranged from 0.45 to 0.47 eV, the interface layer consisted of mainly the native oxide achieved up to 3.0 nm and did not depend on the time of Si electrochemical etching. The evidence that part of the voltage drops on the surface electron states is ensued by comparing the experimental high frequency C-V curves with steady-state I-V curves. Thickening of the porous silicon layer results in a shift in the energetic band of the surface electronic states.

Electrical properties of two kinds of sandwich structures (SnO 2 : F/por-TiO 2 /Ti and Si/por-TiO 2 /Pd) are investigated by the methods of I-V, C-V characteristics and DLTS in vapors of water and alcohol. It has been demonstrated that besides the change of the conductivity and of the capacitance of the por-TiO 2 layers one can also use for gas sensing the change of the high frequency capacitance of the MOS type structure, measurement of the current response at relatively low frequencies and the modification of the charge transfer between the Si bulk and states near the por-TiO 2 /Si interface.

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