Gavrilchenko I. Physical processes in sensor heterostructures on the base of modified porous silicon layers

This thesis is devoted to investigation of physical processes in sensor heterostructures on the base of modified layers of porous silicon and its changes at adsorption of water and alcohol molecules. Based on drift-diffusion equations the influence of water and alcohol vapour adsorption on electric properties of structures of metal- tunnel thin insulator -porSi- Si was theoretically analysed. The value of current at adsorption is obtained as function of effective dielectric constant and inserted charge in porous silicon. The adsorption process model is suggested to explain the nomonotonic behaviour of current at the adsorption of alcohol-water mixture. The conductivity dependence of structure from alcohol concentration has maximum about 40 % alcohol concentration in water solution. The method of determination of porous layer parameters from experimental C-V characteristics is proposed. Effective alcoholmeter is developed on the base of metal-porSi-Si structures. The coefficient of tensoresistive effect in por-Si is negative; it is about in 2.0 times higher than for p-Si slab and increases with por-Si thickness. The last can be explained by gradient of porous silicon porosity. The nomonotonic behavior of accumulation capacitance of Ti-porSi-Si structures (with pores filled by water) is observed in temperature range of Т = -10 ? +10 0С. This effect is explained, first of all, by increasing of internal pressure at water frozen in pores and transformation of electron band of deep levels in porous silicon. The value of internal pressure is estimated. Such pressure results in decreasing of porous silicon bandgap on 0.16 eV. It was established that the photoluminescence intensity and decay lifetime while the porous silicon is exposed to UV illumination are very sensitive to the pH value of the solution. It was substantiated the using of porous silicon as pH-meter in the range of pH changes from 2 to 9. The stability of sensor parameters is increased with modification of porous silicon by polymer PEDOT. The spectral structure of thermo-acoustic emission was investigated in porous silicon structures. It was proposed to use this effect for gas sensors