Low resistive aluminum doped nanocrystalline zinc oxide for reducing gas sensor application via sol–gel process

Abstract

Abstract Aluminum doped zinc oxide films were prepared by a sol–gel process using two different precursors. Zinc acetate and zinc nitrate were used as the starting precursor materials for sol–gel mixtures. The effects of the starting materials on the microstructure, surface morphology, electrical conductivity and gas sensor performance of ZnO were investigated as a function of Al concentration. The results indicated that the crystallite size decreased with the increase of Al dopant concentration from 0 to 5.0 at%. The films prepared by zinc acetate exhibited a skeletal wrinkle structure, which influenced the properties of ZnO films significantly. The gas sensing properties of Al-doped ZnO films prepared by two precursors were investigated for different concentrations of hydrogen in the air. The sensor response, as well as the response and recovery times of ZnO sensors, was analyzed to understand the effect of starting materials on the film quality. It was found that 3.0 at% Al-doped zinc oxide films had optimum properties, such as high electrical conductivity, crystallinity, higher response and faster gas response. Also, the films prepared with the zinc acetate-based precursor exhibited a better performance of gas sensor than those prepared with zinc nitrate-based sol–gel mixtures. Advantages of Al-doped ZnO over undoped ZnO in gas sensors appeared to be (i) low resistive devices, which do not require high impedance peripheral circuits and systems, (ii) tunability of selectivity based on response time constant, and (iii) low operation temperature.