Structural, electrical and optical properties of Al–Ti codoped ZnO (ZATO) thin films prepared by RF magnetron sputtering

Al–Ti codoped ZnO (ZATO) thin films were grown on glass substrates at room temperature by radio frequency (RF) magnetron sputtering technique and annealed under vacuum (∼10−1 Pa) at 400 °C for 3 h. The X-ray diffraction (XRD) patterns show that Al-doped ZnO (ZAO) and ZATO thin films are highly textured along the c-axis and perpendicular to the surface of the substrate. After annealing in a vacuum condition at 400 °C for 3 h, the lowest resistivity of 7.96 and 8.7 × 10−4 Ω cm are observed for ZATO and ZAO films, respectively. But after annealing in air, the resistivity of ZATO and ZAO is higher than 105 Ω cm. In the visible region, the ZAO films show the average transmittance of the order of 90%, while ZATO films were of the order of 75%, which illustrates that the additional Ti doping reduces the optical properties. The optical band gap was found to be 3.46 eV for ZAO film and it increases to 3.53 eV for ZATO films.