Comment on 'A transparent metal: Nb-doped anatase TiO_(2)' Appl. Phys. Lett. 86, 252101 (2005)

摘要

In a recent letter, the resistivity of the Nb-doped anatase TiO_(2) films on (100) strontium titanate (SrTiO_(3)) substrates was measured to be (2-3) X 10~(-4) OMEGA cm at room temperature and showed a metallic feature. Based on their experimental results, Furubayashi et al. claimed that Nb-doped TiO_(2) films were a transparent metal. But the resistivity value of Nb-doped TiO_(2) films on SrTiO_(3) substrates is not reliable due to the Nb diffusion into the SrTiO_(3) substrate at high temperature. Our results show that the resistivity of Nb-doped TiO_(2) films on (0001) sapphire is much higher than that of the films on (100) SrTiO_(3). In our experiment, (100) SrTiO_(3) and (0001) sapphire were used as the substrates for 50 nm Ti_(1-x)Nb_(x)O_(2) (x(velence)0,0.05) thin film deposition. Films were deposited by pulsed laser deposition method in the same experimental condition (1.3 X 10~(-3) Pa oxygen, 820 K) as described in Ref. 1. Electrical properties of the undoped and Nb-doped TiO_(2) on two different substrates were investigated at room temperature. Figure 1 shows two typical current-voltage curves of the two samples on different substrates. When Nb-doped TiO_(2) films were deposited on (100) SrTiO_(3), the measured resistivity was calculated to be in the range of (2-5) X 10~(-4) OMEGA cm, which is in good agreement with the value reported in Ref. 1. But the resistivity of Nb-doped TiO_(2) film on sapphire substrate was found to be as high as 0.5 OMEGA cm, which was much higher than that of the film on (100) SrTiO_(3) substrate.