Low-temperature (10K) micro-cathodoluminescence spectroscopy with a scanning electron microscope was used to probe shallow and deep levels within the grains of Bi2O3-doped ZnO powders prepared under various process conditions. These studies revealed strong electronic state variations between the bulk and boundaries of these sub-micron ZnO grains, including new emissions at about 3.329eV at grain boundaries attributed to Bi phase segregation and/or the formation of new electrically active defects. The characteristic deep-level defect emission at 2.4eV due to non-stoichiometric point defects varied spatially; appearing much stronger in the grain than at the boundaries. The 3.329eV emissions became more pronounced with higher doping concentration and annealing temperature, indicating a strong dependence upon processing. The strong temperature and composition dependence of these boundary-specific features were consistent with the known influence of process conditions on the varistor properties of ZnO powder.

Microcathodoluminescence Spectroscopy of Defects in Bi2O3-Doped ZnO Grains. X.L.Sun, L.J.Brillson, Y.M.Chiang, J.Luo: Journal of Applied Physics, 2002, 92[9], 5072-6