Micrographs and Optical Properties of Al-Doped ZnO Thin Films Deposited by Radio Frequency Magnetron Sputtering

The micrographs and optical properties of Al-doped ZnO (AZO) films deposited by radio frequency (RF) magnetron sputtering are presented in this paper. The AZO films termed as films I, II and III were sputtered on glass substrates heating at 300C, 400C and 500C, respectively. The micrographs, crystal structures and optical properties of AZO thin films were analyzed by using scanning electronic microscopy (SEM) images, X-ray diffraction (XRD) pattern, optical transmission and reflection spectra ranging from 350 to 1000 nm. As the substrate temperature increases to 500C, the film III exhibits a better flatness surface and a larger grain size of ~25nm with a stronger c-axis orientation. The film II has a high transmittance of greater than 92% in the visible light region. We also show that the films II and III have significant red-shift band gap ~3.00 and ~3.13eV, respectively, in comparison with that of the film I (3.31eV). This might be due to the increasing doped Al atoms which do not activate due to segregation at the grain boundaries.