Photoluminescence observations of hydrogen incorporation and outdiffusion in ZnO thin films

ZnO thin films were deposited with the addition of H2 to the reaction gas using the atmospheric-pressure metal organic chemical vapor deposition method. The incorporation and outdiffusion of hydrogen in ZnO films were investigated by comparing the intensity of the hydrogen-related bound-exciton peak (I4: 3.363 eV) in the photoluminescence spectrum. The intensity of I4 peak was found to be the strongest in the ZnO film deposited at 680 °C with H2 present. However, for the ZnO films prepared at the same temperature 680 °C but without H2 present and at the higher temperature of 900 °C with H2 present, respectively, the I4 peak was just a minor shoulder of another bound-exciton peak (I8: 3.359 eV). The intensity of I4 peak in the ZnO films deposited with H2 present was found to decrease with the increasing of annealing temperature. These results suggest that it is difficult for hydrogen to incorporate into ZnO thin films grown at high temperatures even in the hydrogen-present ambient.