Annealing effect on the electrical and the optical characteristics of undoped ZnO thin films grown on Si substrates by RF magnetron sputtering

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 °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 ∼ 800°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.