Epitaxial Co doped BaSnO3 thin films with tunable optical bandgap on MgO substrate

Co doped BaSnO 3 films [BaSn 1 −  x Co x O 3 (0 ≤  x  ≤ 0.50), i.e., BSCO] have been grown on MgO single-crystal substrates via pulsed laser deposition. Effects of the Co-doping level on the crystallinity, the microstructure, and optical properties of the BSCO films are investigated. All the BSCO films are of high crystallinity and grown epitaxially on MgO substrates. The lattice parameter of the (200) plane drops linearly with the increase of the ‘ x ’ value. The Co doping is found to increase the film roughness and the grain size, and a RMS roughness of 8.33 nm and grain size up to 100 nm are observed in the film with x  = 0.50. The low Co-doping level ( x  = 0.05, 0.1) has slight anti-reflection effects on the incident visible light, and the Co-doping level higher than 0.2 reduces the optical transmittance significantly. The optical bandgap shows a first-rising then falling trend with the increase of the Co content, and the lowest bandgap of 1.94 eV is realized in the BSCO film with x  = 0.50.