Thermoelectric and photoconductivity properties of zinc oxide-tin oxide binary systems prepared by spray pyrolysis

摘要

Zinc oxide-Tin oxide (ZnO-SnO) binary thin films were prepared on the glass substrates by spray pyrolysis method. The variation range of the molar ratio of x = [Sn]/[Zn] considered to be changed from 5% to 50%. The films characterized by using the X-ray diffraction (XRD) technique, UV-Vis-NIR spectroscopy, Hall effect, Seebeck effect, electrical and photoconductivity measurements. Using the scanning electron microscopy (SEM) and atomic force microscopy (AFM) images the morphology and roughness of the thin films surfaces were obtained, respectively. AFM micrographs indicate the decrease of roughness by increasing the dopant (Sn) concentration (x). XRD results describe the existence of the ZnO, SnO, SnO_2, ZnSnO_3 and Zn_2SnO_4 phases for various x values. The optical band gap and transmittance were obtained from UV-Vis-NIR spectroscopy results as a function of x. The results show a general band gap narrowing which occurs with the increasing of the Sn concentration which attributed to the structure and many body effects. Moreover, comparing to ZnO thin films, the remarkable decrease of the electrical conductivity and optical transparency were observed at the low x values. The conduction type was determined by the Hall effect and thermoelectric measurements. The Seebeck effect measurements show for ΔT ≤ 185 K, the electrons are the majority carriers, which replaced with the holes for ΔT ＞ 185 K. Power factor quantity was measured as a function of the Sn concentration and temperature. Furthermore, the power factor determines the best x value for the optimal electrical properties. Photoconductivity property was also observed in all samples which weakened for x ≤30%, and increased for the higher x values.