Undoped ZnO films have been grown on Si wafers by RF-magnetron sputtering and have been characterized as a function of annealing temperature (T$_a$) by employing X-ray diffraction, photoluminescence (PL), and Hall effect measurements. The samples were annealed from 500 to 1000 $^circ$C for 3 min under an oxygen ambient in a rapid thermal annealing apparatus. The ZnO films consisted of (100) and (002) polycrystals, and their relative portion changed with varying T$_a$. After annealing at T$_a$ $sim$ 800 $^circ$C, the (100) polycrystals dominantly existed, and the near-band-edge PL peak was most intense, whilst the n-type character was most weakened. We propose that native structural defects play a key role in enhancing the n-type character of ZnO films, judging from the close correlation between the relative intensity of the bound-exciton-related PL lines and the Hall parameters as a function of T$_a$.
Keywords: ZnO films, Photoluminescence, Sputtering, Annealing, Hall effect, X-ray diffraction