Effect of substrate and intermediate layer on the conductivity and charge transport properties of epitaxial BaTiO3−δ films

The conductivity and charge transport behaviors of BaTiO3−δ are usually regulated by physical defect or chemical metal ion doping. In this work, we demonstrated that the conductivity and charge transport properties of epitaxial BaTiO3−δ films can be greatly tuned by using different substrates and intermediate layers between the substrate and BaTiO3−δ film. The temperature dependence of the resistivity experiments show that metallic behavior was observed in BaTiO3−δ films deposited on SrTiO3 substrate. While much higher resistance and semiconductor behavior were observed in BaTiO3−δ films that deposited on MgO and DyScO3 substrates. Additionally, the BaTiO3−δ films' conductivity can be tuned over a wide range from semiconductor to metallic conduction through inserting one intermediate SrTiO3 layer with thicknesses varying from 10 nm to 300 nm. Conversely, the conductivity of BaTiO3−δ films deposited on SrTiO3 substrates can be greatly reduced from metallic to semiconductor conduction through the insertion of one intermediate LaAlO3 film with thickness varying from 0 nm to 150 nm. The different conductivity and charge transport behaviors of BaTiO3−δ films are assumed to be closely related to the oxygen vacancy exchange/blocking effect between BaTiO3−δ film and substrate or intermediate layer.