Studies of defect states of ZnO thin films under different annealing conditions

Abstract

ZnO thin films were grown by the pulsed laser deposition technique on c-plane sapphire substrates at a substrate temperature of 500 degrees C with 1 x 10(-4) Torr ambient gas. After the deposition process, ZnO thin films were annealed at 1000 degrees C for 5 min under N-2 or O-2 ambient gas, respectively. In the X-ray patterns, the (0 0 2) 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 O-2 and N-2 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 E-v+0.594 eV. In addition, a defect state appeared at E-c-0.607 eV, which originated from hydrogen plasma irradiation on the ZnO sample.