Study of sol-gel Cu-doped Al₂O₃ thin films: structural and optical properties

We present a study of of copper-doped Al₂O₃ films prepared by sol-gel deposition. The films were spin-coated on Si and quartz substrates and a high-temperature treatment was conducted in the range 500 – 800 °C in oxygen or nitrogen. The impact was followed of the annealing procedures on the Al_xCu_1-xO₃ films's properties. XRD was used to determine the films' structure; it revealed a mixture of amorphous and crystalline phases. Optical characterization was performed by UV-VIS spectroscopy. The sol-gel films prepared are very transparent. The band gaps of the Al-Cu-O films were estimated from the optical data, with the values ranging from 3.4 to 4.8 eV depending on the Cu content, the annealing and the gas ambients.