We applied cathodoluminescence (CL) spectroscopy to evaluate the defect-induced luminescence within ZnO and Ga-doped ZnO (GZO) nanoparticles. The observed emissions from defect sites present in the GZO lattice exhibited a strong dependence on both dopant content and synthesis methods. The strong and broad defect-induced emissions and inhomogeneous population of intrinsic defects in nano-sized ZnO particles could effectively be suppressed by Ga doping, although large dopant amounts caused the generation of negatively-charged defects, VZn and Oi, with a subsequent increase of the luminescence. Upon deconvolution of the retrieved CL spectra into individual sub-bands, the physical origin of all the sub-bands could be clarified, and related to sample composition and synthesis protocol. This study lays the foundation of quantitative CL evaluation of defects to assess the quality of GZO optoelectronic devices.

A series of high quality zinc oxide (ZnO) nanocrystal films doped with Ge at different Ge/Zn molar ratios were synthesized by the sol-gel method, and structural and compositional changes induced by Ge doping in the ZnO films were analyzed by x-ray diffraction, x-ray photoelectron spectroscopy and cathodoluminescence spectroscopy. Heavy Ge doping in ZnO was found to effectively reduce intrinsic defects in the films and suppress free exciton emission and defect-related emissions in the visible green-red region, by the substitution of Ge at Zn sites and the formation of non-radiative deep-level traps (GeZn)+. The generation of such non-radiative traps was found to be suppressed with respect to the dopant increase, because of a reduction in carrier concentration along with a formation of stable defect complex GeZn–VZn at high doping content. The clarification of defect alterations in Ge-doped ZnO lays the foundation of quantitative evaluation of defect effects on the electrical and optical properties for improving the quality of GeZnO devices.

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