Carrier generation and transport properties of heavily Nb-doped anatase TiO2 epitaxial films at high temperatures

To compare the intrinsic thermoelectric (TE) properties of heavily Nb-doped TiO2 to those of heavily Nb-doped SrTiO3 [S. Ohta , Appl. Phys. Lett. 87, 092108 (2005)], the electrical conductivity (sigma), carrier concentration (n(e)), Hall mobility (mu(Hall)), and Seebeck coefficient (S) of heavily Nb-doped TiO2 (anatase) epitaxial films were measured at high temperatures (300-900 K). The epitaxial films were grown on the (100)-face of LaAlO3 single-crystalline substrates by a pulsed-laser deposition technique at 800 degrees C. The carrier effective mass (m(*)) of the anatase TiO2 epitaxial films was similar to 1m(0), which is an order of magnitude smaller than that of Nb-doped SrTiO3 (similar to 10m(0)). The estimated TE power factor (S-2 sigma) of the similar to 2%-Nb-doped anatase TiO2 film (n(e)similar to 5x10(20) cm(-3)) was similar to 2.5x10(-4) W m(-1) K-2 at 900 K, which is approximately 15% of the 20%-Nb-doped SrTiO3 (1.5x10(-3) W m(-1) K-2). The present findings will help establish a future TE material design concept for Ti-based metal oxides. (c) 2006 American Institute of Physics.