Electrical and structural characterization of as-grown and annealed hydrothermal bulk ZnO

Hall effect measurements in the range 20-370 K on as-grown and annealed hydrothermal bulk ZnO have been performed. The bulk conductivity in the highly resistive as-grown sample was found to decrease and then increase after annealing at 550 degrees C and 930 degrees C, respectively. The conduction in the as-grown material is attributed to a deep donor which is replaced by a much shallower donor after annealing at 930 degrees C. Annealing at both temperatures also produced strong surface conduction effects. Nondegenerate low-mobility surface conduction dominated the electrical properties of the sample annealed at 550 degrees C, while a degenerate surface channel was formed after annealing at 930 degrees C. In addition, Rutherford backscattering and channeling spectrometry (RBS/C) was used to assess the effect of annealing on the crystalline quality of the samples. RBS/C measurements reveal that annealing at 930 degrees C leads to significant improvement of the crystalline quality of the material, while annealing at 550 degrees C results in the segregation of a nonchanneling impurity at the surface.