Microscopic spatial distribution of bound excitons in high-quality ZnO

The surface morphology of the ZnO layers is dominated by a distinct hexagonal domain structure. While the laterally integrated cathodoluminescence spectrum shows intense and narrow I-8 luminescence, a distinct emission line at spectral position of I-0/I-1 emerges in the local spectra taken at domain boundaries. In contrast, no I-0/I-1, emission is found inside the domains. Monochromatic images further evidence the selective incorporation of impurities at the grain boundaries of domains. Monochromatic images of the I-8 peak wavelength directly visualize the strain relaxation across the domains towards their very center, where a drop in quantum efficiency indicates enhanced defect concentration.