  Thermopower (S) for anatase TiO2 epitaxial films (n3D: 1E17-1E21 /cm3) and
the gate voltage (Vg) dependence of S for thin film transistors (TFTs) based on
TiO2 films were investigated to clarify the electronic density of states (DOS)
around the conduction band bottom. The slope of the |S|-log n3D plots was -20
{\mu}V/K, which is an order magnitude smaller than that of semiconductors (-198
{\mu}V/K), and the |S| values for the TFTs increased with Vg in the low Vg
region, suggesting that the extra tail states are hybridized with the original
conduction band bottom.
