STUDY OF ION-BEAM-SPUTTERED ZNO FILMS AS A FUNCTION OF DEPOSITION TEMPERATURE

In this investigation, undoped, ion-beam-sputtered ZnO thin films have been studied as a function of deposition temperature from room temperature to approximately 350-degrees-C. Analysis techniques include x-ray diffraction (XRD), scanning tunneling microscopy, Hall measurement, and spectrophotometry. Hall measurements show that the electrical resistivity of the film decreases with increasing deposition temperature, due to increasing carrier mobility. Additionally, temperature-dependent Hall measurements show that the potential barrier height at the grain boundaries decreases with increasing deposition temperature. By combining data from XRD and Hall measurements, the potential effects of scattering by grain boundaries and ionized oxygen vacancies have been numerically modeled. This analysis indicates that the electron mobility observed in these films is not readily attributed to these scattering mechanisms alone, and other mechanisms, such as point defects within grains, may be present. Optical analysis indicates that transmission in the visible range improves with increasing substrate temperature. Presently, it is speculated that this improved transmission is mainly due to reduced defect levels both within the grains and at the grain boundaries.