Phase transition of ultrasonically sprayed VOx thin films: The role of substrate temperature

Abstract

In this study, vanadium oxide (VOx) semiconductor films were deposited on glass substrates using ultrasonic spray pyrolysis technique. The effect of the substrate temperature on the physical properties of the deposited thin films was investigated. For this purpose, 0.05 M VCl3 aqueous solutions were prepared and sprayed on glass substrates at different temperature of 225 °C, 275 °C, 325 °C and 375 °C. Structural properties of VOx thin films were investigated by taking x-ray diffraction (XRD) patterns and it was determined that the films deposited at 225 °C and 275 °C have tetragonal V4O9 phase while the ones deposited at 325 °C and 375 °C have mixture of α-V2O5 and β-V2O5, α-V2O5 being dominant. The optical band gap energies of the films were determined to be in the range of 2.29 eV to 2.42 eV. Electrical investigations revealed that VOx films have n-type conductivity and electrical resistivity decreased from 4.07 Ωcm to 0.67 Ωcm depending on the increase in substrate temperature. Scanning electron microscopy (SEM) images showed that morphology of the films highly is sensitive to substrate temperature.