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Jianqiao Liu,Guohua Jin,Zhaoxia Zhai,Faheema Fairuj Monica,Xuesong Liu 대한금속·재료학회 2015 ELECTRONIC MATERIALS LETTERS Vol.11 No.3
The grain size effects on tin oxide gas-sensitive elements are numerically described by the model of gradient-distributed oxygen vacancies, which extends the receptor function of semiconductors to the condition of inhomogeneous donor density in grains. The sensor resistance and the response to the reducing gas are formulated as functions of the grain size and the depletion layer width. The simulations show good agreement with the experimental results. The depletion layer width is estimated as 4 nm for the undoped SnO2 element, whereas the values are 2 and 7 nm for Sb-doped and Al-doped samples, respectively. The results are experimentally verified by the donor-doped SnO2 thin films, the depletion layer widths of which are evaluated on the basis of the correlation between the electrical resistance and the Sb-doping amount. The location of the Fermi level is found to be a crucial factor that dominates the evaluation results.
Jianqiao Liu,Zhaoxia Zhai,Guohua Jin,Yuan Li,Faheema Fairuj Monica,Xuesong Liu 대한금속·재료학회 2015 ELECTRONIC MATERIALS LETTERS Vol.11 No.1
The model of gradient-distributed oxygen vacancies is utilized in simulatingthe grain size effects of gas-sensitive SnO2 thin films. The distribution profileof oxygen vacancies has a grain size effect and the profile gradient correlatespositively with the radius of the grains. The simulation results show that thegrain size is a fundamental factor dominating the gas-sensing properties ofthin films. The potential barrier height and resistivity have significant grainsize effects when m is between 0.1 and 0.5 nm−1. The size effects on sensorresponse to stimulant gases can be enhanced by increasing the value of m orthe absolute value of α. Two expressions are used to simulate the grain sizeeffect of the sensor response. The expressions act similarly when α < 0.2. The simplified response provides a neat function to quantitatively explain thesensor performance on gases with low partial pressure. Although the accurate response is complicated, it is applicable to theentire concentration range. A small power-law exponent n is calculated from the accurate response expression when a high gasconcentration is employed, illustrating a “saturation effect” of the response.