Electrical transport properties of epitaxial BaTiO3 thin films

Measurements of the temperature dependent transport properties of epitaxial BaTiO3 are reported. Electrical resistivity and thermoelectric power were measured over the temperature range of 77-300 K. Room temperature resistivities of the as-deposited, undoped films range from 10(5) to 10(8) Omega cm, while values as low as 55 Omega cm are obtained for the La-doped films. The resistivity shows an activated temperature dependence with the measured activation energies ranging between 0.11 and 0.50 eV. The activation energy depends strongly upon the thin film carrier concentration. Thermoelectric power measurements indicate that the films are n-type. The Seebeck coefficient for La-doped BaTiO3 exhibits metallike behavior, with its magnitude directly proportional to temperature. Temperature dependent resistivity and thermopower measurements indicate that the carrier mobility is activated. A transport model is proposed whereby conduction occurs in the La-doped films via hopping between localized states within a pseudogap formed between a lower Hubbard band and the BaTiO3 conduction band edge. (C) 1996 American Institute of Physics.