Studies of defect states of ZnO thin films under different annealing conditions
ZnO thin films were grown by the pulsed laser deposition technique on c-plane sapphire substrates at a substrate temperature of 500C with 110?4Torr ambient gas. After the deposition process, ZnO thin films were annealed at 1000C for 5min under N2 or O2 ambient gas, respectively. In the X-ray patterns, the (002) peak of the annealed sample was shifted from that of the as-grown sample, which indicates a reduced lattice constant of about 1%. Even though the X-ray diffraction patterns in the samples annealed under O2 and N2 annealing gases were almost the same, photoluminescence spectra showed the generation of a shallow level with a few meV, and deep-level states were generated at Ev+0.594eV. In addition, a defect state appeared at Ec?0.607eV, which originated from hydrogen plasma irradiation on the ZnO sample.
defect states of zno annealing effect deep-level transient spectroscopy