Physical Properties of TCO - ZnO Thin Films Sputtered from a Powder Target

Zinc oxide (ZnO) thin films were deposited by RF magnetron sputtering employing a low cost ZnO powder target. In this paper, the effect of the deposition time and the argon pressure on the structural, morphological, electrical, and optical properties of ZnO thin films are described. X-ray diffraction (XRD) results indicated that all the thin films have a preferential c-axis orientation and that the peak position of the (002) plane was shifted to the high 2 theta values as both the deposition time and argon pressure increased. The crystallite size was found to be in the nano range of 20-27 nm, showing that the films are nanostructured in nature. The optical transmittance in the visible region was desirably high (> 85%), the refractive index reached 2.28, and the films demonstrated an optical band gap of about 3.3 eV. The films' resistivity was in the range of 7 x 10(-3) to 8 x 10(-2) Omega.cm. The obtained ZnO films demonstrated the good properties required for transparent conducting oxide applications, namely an enhanced transmission, a reduced average crystallite size, and a reduced resistivity without any doping or post-deposition annealing. Among all of the zinc oxide films obtained in this study, films grown at 1.2 Pa exhibited the best properties for TCO applications: a refractive index of 1.98, an internal stress of 0.5 GPa, and a resistivity of 2.3 x 10(-2) Omega.cm. The results demonstrate that magnetron sputtering from powder targets is a versatile technique for the deposition of high quality transparent conductive ZnO films.