Spatio-time-resolved cathodoluminescence measurements were carried out on low threading dislocation density freestanding GaN substrates grown by hydride vapor phase epitaxy. High-resolution cathodoluminescence imaging allows for visualization of nonradiative recombination channels in the vicinity of accidentally formed inversion domain boundaries. Local cathodoluminescence lifetimes (τCL) for the near-band-edge (NBE) emission are shown to be sensitively position dependent. A linear relation between the equivalent internal quantum efficiency (ηinteq) and τCL for the NBE emission was observed at room temperature under a weak excitation condition, and spatially resolved excitation led to the observation of the highest ηinteq of 20 with τCL of 3.3 ns.
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