Microcathodoluminescence spectroscopy of defects in Bi[sub 2]O[sub 3]-doped ZnO grains.

Low-temperature (10 K) microcathodoluminescence spectroscopy with a scanning electron microscope has been used to probe shallow and deep levels within the grains of Bi[SUB2]O[SUB3]-doped ZnO powders prepared under different process conditions. These studies reveal strong electronic state variations between the bulk and boundaries of these submicron ZnO grains, including new emissions at ~3.329 eV at grain boundaries attributed to Bi phase segregation and/or the formation of new electrically active defects. The characteristic deep level defect emission at 2.4 eV due to nonstoichiometric point defects varies spatially, appearing much stronger in the grain bulk than at the boundaries. The 3.329 eV emissions become more pronounced with higher doping concentration and annealing temperature, indicating a strong dependence on processing. The strong temperature and composition dependence of these boundary-specific features are consistent with the known influence of process conditions on the varistor properties of ZnO powder. [ABSTRACT FROM AUTHOR]