| Summary: | <p>In this work we study the effect of transport mechanism of charge carriers on the conductivity of metal oxide semiconductor (MaS) thin films due to gas adsorption within the framework of diffusion theory of point defect which uses the concept of small polarons and polarons as charge carriers . Here we have introduced the theory of point defect in Flockhardt's models for the MaS surfaces in order to analyze the adsorption effect of reductor gases (C2HsOH, NH3 and CO) and oxidator gases (02 and C02) on MaS .conductivity. Formulation for the conductivity was proposed in thermodynamic equilibrium states between MOS surfaces and bulk materials by considering the operation temperature of thin film gas sensor. In line with polaron and small polaron characteristics then, instead of using Fermi-Dirac statistics, we have assumed in our model that the particle systems are governed by the classical Maxwell-Boltzmann statistics. Application of both point defect and diffusion theories lead to theoretical models which shows that conductivity of gas adsorption depends on oxygen pressure (p), concentration of testing gas (C) and material temperature (T).</p>
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