Effect of annealing temperature on the microstructure and optical–electrical properties of Cu–Al–O thin films

• CuAlO2 phase has been obtained by RF magnetron sputtering method with the following annealing treatment.
• The microstructure and optical–electrical properties of the films are affected significantly by the annealing temperature.
• The relation between the CuAlO2 phase formation and the annealing temperature has been established.

We have successfully prepared Cu–Al–O thin films on silicon (100) and quartz substrates by radio frequency (RF) magnetron sputtering method. The as-deposited Cu–Al–O film is amorphous in nature and post-annealing treatment in argon ambience results in crystallization of the films and the formation of CuAlO2. The annealing temperature plays an important role in the surface morphology, phase constitution and preferred growth orientation of CuAlO2 phase, thus affecting the properties of the film. The film annealed at 900 °C is mainly composed of CuAlO2 phase and shows smooth surface morphology with well-defined grain boundaries, thus exhibiting the optimum optical–electrical properties with electrical resistivity being 79.7 Ω·cm at room temperature and optical transmittance being 80% in visible region. The direct optical band gaps of the films are found in the range of 3.3–3.8 eV depending on the annealing temperature.