High transparent and conductive ZnO thin films doped with Ti

Highly conductive and transparent impurities-doped zinc oxide thin films have recently gained much attention because they are composed of inexpensive, abundant materials. The Ti doping ZnO thin films were deposited by simultaneously magnetron co-sputtering from both Zn and Ti targets in a mixture of oxygen and argon gases onto heated Corning 7059 glass substrates. By adjusting the Ar/O₂ ratio and other process parameters including RF power, and substrate temperature, the electrical property of ZnO thin films changes from an isolation to a good conduction. The results show that deposition rate is an approximately linear function of DC power of Ti target except at 300 watts. At 300 watts, the growth rate decreases may due to strong interference between zinc and titanium sputtered atomic fluxes. The proud (002) diffraction peak is found in the XRD(X-ray diffraction) patterns of the deposited ZnO films which demonstrates a strong preferred orientation existing in the films. The incorporation of titanium atoms into zinc oxide films is not effective until the Ti target power increased to a value of 250watts. The atomic percents of titanium in the films are measured to be 1.33% and 2.51% corresponding to 250watts. and 300watts of applied Ti target power respectively. The XRD patterns shown only a single ZnO phase existing and shifted to lower 2 theta values imply Ti atoms incorporated into the ZnO lattice and occupy the zinc atoms lattice sites. Because the oxidation number of Ti ion is higher than zinc ion, the resistivity is expected lowered due to extra carriers beside the native oxygen vacancies. The reistivity of undoped ZnO films is extremely high and decrease to a value of 3.78 × 10^-2 ohm-cm when 2.51% atomic percent of Ti is incorporated. All of the zinc oxide films show good transmittance in the range of 4000-7000 angstrom. The average transmittance is 70-80% in this study. The optical energy gap increases with increasing the doping amount of Ti in the films. The maximum value of optical energy gap gained in this study is 3.18 eV when the doping amount of Ti is 1.33 atomic %.