We have investigated the transport properties and electronic states of W-doped anatase TiO2 (Ti1-xWxO2) fabricated by pulsed-laser deposition. Based on transport and photoemission spectroscopy (PES) measurements, we discuss the conduction mechanism of Ti 1-xWxO2, focusing on the valence state of W. The Ti0.95W0.05O2 film deposited under optimized conditions showed a resistivity of 2× 10-3 ωcm at room temperature, which is approximately ten times higher than that of Ti0.94Nb0.06O2. This is mainly due to the lower carrier density in Ti1-xWxO2 films. From PES measurements of Ti0.91W0.09O2 films, we observed the finite density of states originating from O 2p hybridized with W near the top of the valence band. However, we could not find any states at the same position in the Ti0.94Nb0.06O2 films. In addition, the density of states near the Fermi level [N(EF)] was found to be quite low in the Ti0.91W0.09O2 films. Indeed, this is in sharp contrast to Ti0.94Nb 0.06O2, which indicates a remarkably high N(EF) value assigned to the bottom of the Ti 3d conduction band. The difference in transport properties between Ti1-xWxO2 and Ti1-xNbxO2 can be attributed to the existence of impurity states that trap carriers associated with doped W atoms.
ASJC Scopus subject areas
- Physics and Astronomy(all)