ESR studies of hydrogen-induced paramagnetic defects in polycrystalline ZnO films

The hydrogen doping effect was investigated in polycrystalline ZnO and ZnO:H thin films prepared by the photoassisted metalorganic chemical vapor deposition (photo-MOCVD) technique. In situ post-deposition hydrogen doping was provided using mercury sensitized photodecomposition of hydrogen gas. The structure and morphology of the films were monitored by XRD and FTIR measurements. The studies of paramagnetic defects in as-grown and hydrogenated ZnO thin films were undertaken in the temperature range 77–300 K using X-band ESR spectrometer. It was found that all the samples exhibit a single strong Lorentzian line at g = 1.956. The line intensity was shown to increase upon H-doping. The concentration of paramagnetic defects in the samples, associated with shallow donors, was found to be 8.2 × 1017 cm−3 for as-grown ZnO and 1.9 × 1018 cm−3 for hydrogen treated ZnO:H thin films. The nature of broadening of ESR line in polycrystalline ZnO thin films due to the surface effects is discussed.