Structural and electrical properties of ZnO thin films deposited by atomic layer deposition at low temperatures

In this study, ZnO thin films were deposited by atomic layer deposition (ALD) at various process temperatures. The purpose of this paper was to investigate the controllability of the preferred orientations of ZnO thin films by varying the process temperature and to determine the effect of the preferred orientations on the electrical properties of the films. The process temperature was varied from 70 to 250°C at several increments while the other ALD process parameters were fixed. The deposition rates and uniformities, crystal structures, and electrical properties of these films were evaluated at the various process temperatures. At process temperatures of 70 and 90°C, ZnO thin films showed strong (002) preferred orientations with cylindrical, fine, columnar crystal structures, almost a 1:1 stoichiometric chemical ratio of Zn to O, and n-type carrier concentrations in the range of 1016 cm-3 with resistivities of 0.1-1 cm. ZnO thin films deposited at temperatures higher than 110°C had wedge-shaped crystal structures, high oxygen deficiencies, and higher n-type carrier concentrations up to 1020 cm-3 than the films deposited at lower temperatures.