Optical and gas sensing properties of Al-doped ZnO transparent conducting films prepared by sol-gel method under different heat treatments

Al-doped ZnO transparent conducting films were prepared on quartz substrate by the sol-gel method using zinc acetate dehydrate, aluminum nitrate nonahydrate, ethanol and monoethanolamine (MEA) under different heat-treating processes. The evolution of structural, morphological, optical and electrical properties was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), UV-vis spectrophotometer and four-probe instrument. The analyzed results indicate that the obtained films are of good crystal quality with the wurtzite-type ZnO structure and a highly c-axis preferred orientation. The thin films with the different surface morphologies and thicknesses were obtained under the different heat-treating processes. After post-heating treatment, the energy band gap decreases from 3.21 eV to 3.14 eV and the resistivity from 3.22 Omega cm to 1.42 Omega cm, while the average transmittance in the range of 400-700 nm increases from 82.9% to 86.7%. As-prepared Al-doped ZnO thin films were used directly as a sensing device to investigate the sensing properties in ethanol atmosphere. The home-built Al-doped ZnO thin film sensors showed high response, fast response, and recovery times toward ethanol gas, making these thin films not only interesting for sensor devices, but also for a number of related electrochemical applications. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.