Electrical and optical properties of strongly reduced epitaxial BaTiO3−x thin films

A series of BaTiO3−x (x=0, 0.07, 0.18, and 0.48) thin films with c-axis oriented tetragonal perovskite structures were epitaxially grown on SrTiO3 (100) and MgO (100) substrates by laser molecular-beam epitaxy under various oxygen pressures. The electrical conductivity of the deposited thin films increases with decreasing the oxygen pressure. A metallic conduction is observed in the oxygen most deficient BaTiO2.52 thin film whose oxygen content (2.52) and electrical resistivity (6.0×10−5 Ω cm) are both the minimum values among literature. An optical absorption peak is observed in each oxygen deficient BaTiO3−x thin film. The peak position shifts to lower energy, and the peak width becomes larger with decreasing the oxygen pressure. The influence of oxygen pressure on the electrical and optical properties in the reduced BaTiO3−x thin films is discussed.