Pulsed laser deposition of β-NaGaO2: significant dependence of sodium fraction, morphology, and phases of the film on deposition position in the plume

Abstract

Abstract Thin films of β-NaGaO2, a precursor material of β-CuGaO2, were fabricated using pulsed laser deposition. The phase and morphology of these films depended on the deposition position, i.e., the target-substrate distance and distance from the central plume axis. Three phases appeared in the films, namely a Na-deficient and stoichiometric β-NaGaO2, amorphous with a Na fraction with total cations, x Na, of ∼0.375, and an unidentified phase with x Na of ∼0.57. These three phases formed four characteristic textures. The variation in phase and morphology is discussed and explained in terms of the spatial distribution of the Na fraction and kinetic energy of ablated particles deposited on the substrate. By using the obtained stoichiometric β-NaGaO2 film, a stoichiometric β-CuGaO2 film was successfully fabricated. Its energy band gap was determined to be 1.64 eV, which is approximately 0.1 eV larger than that previously reported for Cu-deficient β-Cu0.9GaO2−δ .