Rapid formation of transparent CuAlO2 thin film by thermal annealing of Cu on Al2O3

An 850-nm-thick CuAlO2 film was formed by solid state reaction of evaporated thin film Cu on c-cut Al2O3 (sapphire) at 1200 °C for reaction times as short as 10 min. X-ray diffractogram confirms the formation of (0 0 l) CuAlO2, indicating oriented growth of CuAlO2 on c-cut Al2O3. Fourier transformation infra-red (FTIR) spectra showed peaks corresponding to Cu–O, Al–O and O–Cu–O bonds, confirming further the CuAlO2 phase formation. UV–visible spectrum measurement showed high transparency of the film in the visible region with a direct band gap of 3.25 eV. The mechanism of the formation of the film is discussed.