Effect of the substrate temperature on the properties of ZnO films grown by RF magnetron sputtering

Zinc Oxide films were deposited by RF magnetron sputtering using a zinc oxide target with different substrate temperatures. The structural characteristics of the films were investigated by X ray diffractometry (XRD) and scanning electron Microscopy (SEM), while the electric and optical properties of the films were studied by the impedance spectroscopy and optical spectroscopy, respectively. It was shown that all of the films deposited have a c-axis preferred orientation perpendicular to the substrate. As the temperature of the substrate increased, the crystallinity was enhanced and the grain size was increased. Furthermore, the electrical resistivity was decreased. However, the optical transmittance of about 80% was maintained over the substrate temperature range. The electrical ac impedance spectroscopy data showed distinct arcs from lowest (Hz) frequency to highest (MHz) frequency due to the contribution of the grain and grain boundaries to the mechanism of the charge transfer in the material. The conduction is dominated by the grain boundary effect at low substrate temperatures while at high temperatures, the contribution of the grains is predominant. This paper describes the utility of these techniques, their theory and use for controlling the material properties, the issues that we are addressing to develop a gas sensor prototype knowing the best operating frequency of the sensor and the optimum crystalline structure. (C) 2003 Elsevier B.V. All rights reserved.