Figure 4 Transmission spectra of TZO films with various Ti concentrations. The inset shows the plot of (αhv)2 versus hv. To investigate the electrical properties of the TZO thin films, Hall measurements are carried out at room

temperature. The thermally grown SiO2 was chosen as the substrate since the substrate needs to be insulative. The dependence of carrier density, resistivity, and mobility on Ti contents in the TZO films is shown in Figure 5. It should be noted that the resistivity of the sample with N = 1 is so large that its mobility and carrier concentration cannot be measured accurately. As is displayed, the resistivity, mobility, and carrier concentration for pure ZnO films prepared by ALD are 2.14 × 10−3 Ω cm, 1.4 × 1020 cm−3, and 22.5 cm2/V · s, respectively. The resistivity of the TZO film with N = 20 Bucladesine ic50 selleck chemicals llc at first drops to a minimum value of 8.874 × 10−4 Ω cm and then goes up with the increase of the Ti contents. It suggests that the conductivity of ZnO film can be improved significantly with appropriate Ti doping concentration. On the other hand, the maximum carrier concentration of 6.2 × 1020 cm−3 is achieved for the sample with N = 10, which is higher than that reported by Park and Kim [22]. However, carrier concentration

of the TZO film undergoes an abrupt drop when more Ti impurities are introduced into the TZO film. The decrease in the carrier concentration can be interpreted as follows: As the Ti doping concentration continues to increase, some titanium atoms tend to aggregate near grain boundaries to form TiO2 CH5183284 instead of taking the place of Zn2+ to generate more free carriers [23]. The widening of band Teicoplanin gap is also generally considered as a dominant mechanism contributing to the decrease of carrier concentration [20, 21]. In addition, the mobility of TZO films decreases from 21.7 cm2/s for pure ZnO to 2.3 cm2/s for the sample with N = 2. The decrease in

mobility is apparently due to the increase of carrier scattering, the deterioration in the crystalline quality, and formation of TiO2 at the grain boundaries. Figure 5 Resistivity, mobility, and carrier concentration of the TZO films deposited on thermally grown SiO 2 . Conclusions Ti-doped ZnO thin films with the thickness of around 100 nm were prepared by ALD at 200°C. The fact that film thicknesses measured by spectroscopic ellipsometry were thinner than expected for samples with ALD cycle ratio of ZnO/TiO2 less than 10 suggested a hampered growth mode of ZnO on TiO2 layer. TZO films synthetized by ALD crystallized preferentially along the [100] direction. High transparency (>80%) in the visible region was obtained, and the band gap of the TZO films increased with increasing Ti doping concentration due to the Burstein-Moss effect. It was observed that the resistivity of TZO film had a minimum value of 8.