Role of oxygen in structural properties of annealed CuAlO2 films

CuAlO₂ films were sputtered on quartz substrates at different oxygen partial pressures (OPP) and carried out the annealing at 900 °C for 5 h in N₂ ambient. The structural properties of these films have been studied in detail by X-ray diffraction, Raman spectroscopy, and atomic force microscopy. Annealed CuAlO₂ films are grown along the (0 0 1) preferential orientation. The film deposited at 20% OPP demonstrates the excellent crystalline behavior and the smallest electrical resistivity (41.8 Ω cm). At higher OPP, the crystalline behavior begins to degenerate up to the amorphous state at 60% OPP, and some micro-caves presented in the film surface become larger and deeper with the increase in OPP. We believe that the negative thermal expansion behavior associated with excess oxygen atoms is the primary responsibility for the change in structural properties.