Structure and optical properties of La-doped ZnO thin films at room temperature

La-doped ZnO (with 0, 1, 5 and 7 wt.% La) thin films were deposited on Si substrates by ultrasonic spray pyrolysis, using frequency of 1.7 MHz, and heated at 450 °C for 15 min. The effect of La addition on the structural and optical properties of ZnO thin films was analysed. X-ray diffraction patterns confirmed that all prepared thin films had a polycrystalline hexagonal wurtzite structure with highly preferred texture in the (002) plane in the case of the ZnO containing 7 wt.% La. Atomic force microscopy analyses confirmed that the surface morphology is affected by La addition and the root mean square (RMS) roughness tended to be higher by increasing La content. The optical band gap energies of the La-doped thin films are smaller than that of the undoped ZnO. The photoluminescence properties of the prepared thin films confirmed that there was a significant redshift of DLE to wavelength of 711 nm when 1 wt.% of La was incorporated in ZnO structure. It was proposed that the incorporation of La into the ZnO structure caused the oxygen atoms to have a strong bond with La.