Direct evidence for selective impurity incorporation at the crystal domain boundaries in epitaxial ZnO layers

A direct correlation of structural properties with the spatial distribution of bound exciton luminescence in ZnO epitaxial layers has been achieved on a microscopic scale using highly spatially and spectrally resolved cathodoluminescence. The morphology of the high quality ZnO layer is characterized by a distinct domain structure. While the laterally integrated cathodoluminescence spectrum shows narrow (full width at half maximum <3 meV) I-8 luminescence, a pronounced emission line at I-0/I-1 emerges in the local spectra taken at domain boundaries. In complete 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. Micro mappings of the I-8 peak wavelength directly visualize the strain relaxation across the domains toward their very center, where a drop in quantum efficiency indicates enhanced defect concentration. (C) 2004 American Institute of Physics.