Influence of hydrogen introduction on structure and properties of ZnO thin films during sputtering and post-annealing

Abstract

ZnO thin films were prepared in Ar and Ar+H2 atmospheres by rf magnetron sputtering, and then they were annealed in vacuum and Ar+H2 atmosphere, respectively. The structure and optical–electrical properties of the films were investigated by X-ray diffraction, transmittance spectra, and resistivity measurement, and their dependences on deposition atmosphere, annealing treatment, and aging were studied. The results showed that adding H2 in deposition atmosphere improved the crystallinity of the films, decreased lattice constant, increased band gap, decreased the resistivity by the order of 104Ωcm, but exhibited poor conductive stability with aging. After Ar+H2 and vacuum annealing, crystallinity of the films deposited in Ar and Ar+H2 was further improved; their resistivity was decreased by the order of 105 and 101Ωcm, respectively, and exhibited high conductive stability with aging. We suggest that the formed main defect is VO and Hi when H2 is introduced during deposition, which decreases the resistivity but cannot improve the conductive stability; hydrogen would remove negatively charged oxygen species near grain boundaries during Ar+H2 annealing to decrease the resistivity, and grain boundaries are passivated by formation of a number of VO–H complex (HO) to improve the conductive stability at the same time. Under vacuum annealing, the hydrogen that is introduced non-intentionally from deposition chamber maybe plays an important role; it exists as HO in the films to improve the conductive stability of the films.