Grain size dependence of electrical and optical properties in Nb-doped anatase TiO2

Anatase thin films of pure TiO2 and 6% niobium doped TiO2 (Nb:TiO2) were fabricated on LaAlO3(100) by pulsed laser deposition. The electrical properties of Nb:TiO2 films are grain-size dependent, i.e., the larger grain size, the higher conductivity, and mobility. For all TiO2 and for Nb:TiO2 with small mean grain size (d<15 nm), the band gap energy is found to increase systematically with the decrease in d, which is consistent with the quantum confinement model. For the films with large mean grain size (d>15 nm), particularly, a blueshift in Nb:TiO2 is governed by the Burstein–Moss effect.