Ethanol and Water Vapors Sensing by MIS-Structure with Porous Intermediate Layer

摘要

The MIS-type humidity sensor and alcohol - meter based on metal-organic layer-porous silicon (PS) - silicon were elaborated. The influence of the adsorption of ethanol/water mixture on conductivity and capacity voltage (C-V) characteristics was analyzed theoretically and investigated experimentally. The highest response is reached at about 40% concentration of ethanol in water. Such a form of the dependence can be explained by the fact that the adsorption of ethanol and water vapors influences the PS in different ways. The adsorption of donor-type water molecules on the PS surface results in an increase of the conductivity due to the injection of free electrons. The adsorbed on the PS surface the ethanol molecules, on the one hand, prevent the water molecules adsorption and, on the other hand, change the surface recombination rate. The MIS structures with complex dielectric interface (PS + organic layer) show the increased response to the presence of water and ethanol in comparison with structures of metal-PS-Si. To estimate the effect of pores filling/empting on sensors response/recovery time the test PS Bragg mirror was formed and time-depended reflectivity during the adsorption/desorption process was measured.