Modified MIS‐structure based on nanoporous silicon with enhanced sensitivity to the hydrogen containing gases

Abstract

AbstractThe gas sensitivity of metal‐insulator‐semiconductor (MIS)‐structures based on nanoporous silicon with active electrodes from palladium/tungsten oxide composite has been studied. It was found that the using of palladium/tungsten oxide composite (instead of thin palladium film) leads to enhanced sensitivity of MIS structures to hydrogen sulphide in air. The mechanism of this phenomenon has been established. The enhanced H2S sensitivity is explaind in the following way. The microparticles of tungsten trioxide inside palladium matrix stimulate the dissociation of hydrogen sulphide molecules, and hydrogen atoms and/or protons flow down to palladium surface, are absorbed by palladium volume, diffuse to palladium/oxidized nanoporous silicon interface. Hydrogen atoms adsorbed at the interface are polarized and give rise to a dipole layer. As a result, the voltage shift of the capacity‐voltage (C‐V) curve proportional to the measured gas concentration is observed. The surface microstructure of Pd/WO3 composite was studied by AFM microscopy. The chemical content of the composite film has been investigated by SIMS. It was found that the composite film on nanoporous silicon surface poses the holes with the size about 0.05 μm, the mean separation between tungsten oxide microparticles is 1‐2 μm. It also was found that the using of the additional double layer polymer film (polymer film (phthalocyanine zinc)/semicon‐ductor film (cadmium sulphide)) on composite film surface leads to the additional enhancement of the gas sensitivity to hydrogen sulphide. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)