Crystalline state and temperature-dependent conductivity of annealed ITO thin films

Mixed In₂O₃and SnO₂thin films were deposited by using an RF magnetron sputtering method. The films were annealed at 150 °C, 300 °C, and 450 °C for 1 h, and the structural, optical, and electrical properties of the films were investigated. The crystalline structure of ITO (indium tin oxide) is well formed on the films annealed at 300 °C and 450 °C. As the annealing temperature is increased, the crystallinity and the grain size are found to be improved. The average transmittance of the ITO films in the visible range, where the determined band-gap energies of the ITO films at annealing temperature 300 °C and 450 °C are 3.86 and 3.96 eV, respectively, is over 90%. The temperature-dependent resistivity shows metallic behavior down to 150 K and fits well with the Bloch-Grüneisen equation. The negative temperature coefficient of resistivity below the metallic region is caused by the Coulomb interaction, which decreases with increasing annealing temperature.