Effect of substrates and post-deposition annealing on rf-sputtered Al-doped ZnO (AZO) thin films

Al-doped zinc oxide (AZO) thin films were deposited on glass, quartz, and indium tin oxide (ITO) substrates using rf magnetron sputtering. The influence of the substrate material and post-deposition annealing (300–700 °C) in air on the structural, optical and electrical properties were studied. All as-deposited and annealed films were investigated using X-ray diffraction (XRD), grazing incidence XRD, field effect scanning electron microscope, Raman spectroscopy, UV–visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), and four-point probe measurements. The AZO films were crystalline and preferentially oriented along the (002) diffraction plane. The average crystallite size decreased with annealing temperature and ranged from 19.6 to 30.3 nm. The AZO films were non-porous, dense, and continuous with columnar growth. The prominent Raman peaks showed anomalous doped ZnO modes. The deconvoluted Raman spectra showed the presence of A₁ (LO) and A₁ (TO) ZnO modes. FTIR revealed the Al–O and Zn–O stretching vibrations in the films. AZO films had high optical transmittance (61 to 78%) at visible wavelengths and an average band gap of 3.27 ± 0.04 eV, which is suitable for optoelectronics applications. The resistivity (4.5 × 10⁻⁴ to 9 × 10⁻⁴ Ω cm) and high figure of merit value indicates that AZO thin films may be suitable transparent conductive oxides.