Wet-chemical dip-coating preparation of highly oriented copper–aluminum oxide thin film and its opto-electrical characterization

Transparent p-type semiconducting copper aluminum oxide thin film has been synthesized by a wet-chemical route. CuCl and AlCl3, dissolved in HCl, are taken as starting materials. pH value of the solution is controlled by adding a measured amount of NaOH into it. Films are deposited by dip-coating technique on glass and Si substrates followed by annealing in air at 500 °C for 3 h. XRD pattern confirms the crystalline CuAlO2 phase formation in the film and also indicates a strong (0 0 6) orientation. UV–vis spectrophotometric measurements show high transparency of the film in the visible region with a direct allowed bandgap of 3.94 eV. Electrical measurements depict the thermally activated conduction within the films. Thermoelectric measurements confirm the p-type nature of the films. Compositional analysis shows the presence of excess (nonstoichiometric) oxygen within the material, which is incorporated during the air-annealing of the film. According to defect equilibrium, this excess oxygen is predicted to cause the p-type conductivity of the film. This type of cost-effective solution-based technique is very useful for volume production of this kind of technologically important material for transparent electronic and other diverse applications.