Preparation And Optoelectrical Properties Of Zinc Titanium Oxide Transparent Semiconductor Thin Films

Indium tin oxide(ITO) has been widely employed as transparent electrodes in optoelectronic devices since it has high visible transmittance, low resistivity, chemical stability and relatively high work function. However, indium is rare metal and reserve volume is scare, which limits its application. Zinc oxide(ZnO) is a kind of wide band bandgap semiconductor material with low resistivity, high transmittance, excellent optical and electrical properties. It can be easily prepared in a variety of structure and excellent performance film. Besides, the cost of ZnO is much cheaper than the cost of ITO, and non-toxic advantage makes it is preferred than other oxide thin film. In recent 20 years, the fabrication of ZnO films has attracted a considerable amount of interest. It was widely used in many applications, such as solar cells, flat-panel displays, light-emitting diodes and gas sensors.In this paper, zinc titanium oxide(TZO) transparent semiconductor thin films were deposited on the glass substrates by radio-frequency magnetron sputtering technique. The microstructural, optical, electrical and optoelectronic properties of TZO films were measured by XRD, XPS, UV-visible spectrophotometer and four-point probe, respectively. The main works and conclusions are as follows:(1) The effect of substrate temperature on microstructural, optical and electrical properties was studied. The deposited TZO thin films exhibit a polycrystalline wurzite structure with a preferred orientation along the(002) plane. The TZO thin film deposited at the substrate temperature of 410 K possesses the best optoelectronic properties, with the highest average visible transmittance of 76.21% and the maximum figure of merit of 3.17×103 S·cm-1.(2) The sputtering pressure has an important impact on structural property, too small pressure or too large pressure caused bad crystallinity. When the sputtering pressure is 0.6 Pa, the TZO thin film possesses the lowest resistivity of 1.15×10-3 ?·cm and the maximum figure of merit of 3.17×103 S·cm-1.(3) With the increase of the target-substrate distance, the average visible transmittance and resistivity decrease, while the optical bandgap and figure of merit increase. When the target-substrate distance is 75 mm, the TZO thin film exhibits better optoelectronic properties, with higher figure of merit of 2.67×103 S·cm-1 and larger optical bandgap of 3.47 eV.(4) The genetic algorithm was used in calculating the optical constants(the refractive index and extinction coefficient) of the TZO thin film. The result shows that the refractive index decreases with the increase of wavelength, and the deposited TZO films possess the normal dispersion characteristics in the visible region. The refractive index dispersion curve of thin films obeys the single oscillator model.(5) The optimum conditions of TZO transparent semiconductor thin films in our work are shown as follows: substrate temperature, 410 K; target-substrate distance, 75 mm; working pressure, 0.6 Pa; sputtering power, 200 W and sputtering time, 20 min.