Co-doping effect of Ca and N on the structure and properties of CuAlO ₂ thin film

Ca-doped CuAlO₂ films were prepared by the radio-frequency magnetron sputtering technique. As shown by X-ray diffraction measurements, single-phase hexagonal CuAl_1-xCa_xO₂ is formed for Ca concentrations up to 1.5 atom %. Hall measurements confirm the p-type conduction for all films. The introduction of Ca leads to a sharp improvement in electrical conductivity due to the increase in carrier concentration. With increasing doping concentrations, the bandgaps of CuAl_1-xCa _xO₂ thin films increase. We attribute this to Burstein-Moss shift from increased carrier concentrations. A nitrogen plasma treatment results in further enhancement of the electrical conductivity due to introducing N as an acceptor into CuAl_0.985Ca_0.015O ₂ thin film.