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We investigate the impact of threading dislocations with an edge component (aor a+c-type) on carrier recombination and diffusion in GaN(0001) layers closeto the surface as well as in the bulk. To this end, we utilizecathodoluminescence imaging of the top surface of a GaN(0001) layer with adeeply buried (In,Ga)N quantum well. Varying the acceleration voltage of theprimary electrons and comparing the signal from the layer and the quantum wellenables us to probe carrier recombination at depths ranging from the closevicinity of the surface to the position of the quantum well. Our experimentsare accompanied by fully three-dimensional Monte Carlo simulations of carrierdrift, diffusion, and recombination in the presence of the surface, the quantumwell, and the dislocation, taking into account the dislocation strain field andthe resulting piezoelectric field at the dislocation outcrop. Near the surface,this field establishes an exciton dead zone around the dislocation, the extentof which is not related to the carrier diffusion length. However, reliablevalues of the carrier diffusion length can be extracted from the dipole-likeenergy shift observed in hyperspectral cathodoluminescence maps recorded aroundthe dislocation outcrop at low acceleration voltages. For high accelerationvoltages, allowing us to probe a depth where carrier recombination isunaffected by surface effects, we observe a much stronger contrast thanexpected from the piezoelectric field alone. This finding provides unambiguousexperimental evidence for the strong nonradiative activity of edge threadingdislocations in bulk GaN and hence also in buried heterostructures.

Carrier diffusion in GaN -- a cathodoluminescence study. III: Nature of nonradiative recombination at threading dislocations