Effect of niobium doping on the optical and electrical properties in titanium dioxide grown by pulsed laser deposition

The influence of niobium (Nb) on both the electrical and optical properties in titanium dioxide (TiO2) grown by pulsed laser deposition was investigated. Nb atoms with a critical doping ratio of 8 at. % were carefully controlled in a 100 nm-thick TiO2 layer (Nb:TiO2). The Hall effect results revealed that the electrical resistivity and electron concentration of the resulting Nb:TiO2 film were 30 times lower and 2 orders of magnitude higher than those of un-doped TiO2 (u-TiO2), respectively, leading to a slight degradation of optical transmittance in the visible region. The room temperature photoluminescence results showed that the emission intensity at the near band of Nb:TiO2 was greatly enhanced, while, that at the impurity band created by oxygen vacancy (Vo) was almost constant. Detailed investigation of the T-dependent conductivity indicated that the Nb:TiO2 film possessed an activation energy as shallow as 20.8 meV, which suggested that the electrical properties were dominantly determined by Nb shallow impurity rather than point defects such as Vo.