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Herein, the use of cathodoluminescence (CL) hyperspectral mapping in the quantification of the AlGaN alloy composition in graded buffer structures is explored. The quantification takes advantage of the known parabolic dependence of the AlGaN bandgap on the alloy composition allowing the AlGaN near‐band‐edge (NBE) emission energy recorded from CL to be converted to a composition. The proposed quantification method is first applied to cleaved cross‐sections of two nominally step‐graded AlGaN buffer structures each containing five AlGaN layers with different compositions. By comparing the compositions obtained from CL to those calculated using X‐ray diffraction, a close agreement between values from both techniques is observed. However, due to a change in the bowing parameter, some deviation is observed for layers with compositions near 75%. The method is then applied to cleaved cross‐sections of an AlGaN buffer whose group III precursor flow molar ratio is varied linearly throughout the growth. Herein, the hyperspectral nature of the CL datasets is exploited such as to produce composition maps by converting the relevant AlGaN‐NBE emission energy at each pixel of the CL data to a composition.

Core-shell nanorod based light-emitting diodes (LEDs) with their exposed non-polar surfaces have the potential to overcome the limitations of planar LEDs by circumventing the quantum confined stark effect. In this experiment, InGaN/GaN core-shell nanorods were fabricated by a combination of top-down etching and bottom-up regrowth using metal-organic vapour phase epitaxy. When viewing the nanorods along their long axis, monochromatic cathodoluminescence maps taken at the GaN near-band-edge emission energy (3.39 eV) reveal a ring-like region of lower emission intensity. The diameter of this ring is found to be 530 (±20)nm corresponding to the ∼510 nm diameter nickel etch masks used to produce the initial GaN nanopillars. Thus, the dark ring corresponds to the regrowth interface. To understand the origin of the ring, scanning transmission electron microscopy (STEM) and cathodoluminescence (CL) hyperspectral mapping at 10K were performed. STEM imaging reveals the absence of extended defects in the nanorods and indeed near the regrowth interface. Monochromatic CL maps recorded at 10K show that the ring remains dark for monochromatic maps taken at the GaN near-band-edge emission energy (3.47 eV) but is bright when considering the donor-acceptor pair emission energy (3.27 eV). This peculiar anticorrelation indicates that the dark ring originates from an agglomeration of point defects associated with donor-acceptor pair emission. The point defects are incorporated and buried at the GaN regrowth interface from the chemical and/or physical damage induced by etching and lower the radiative recombination rate; limiting the radiative efficiency close to the regrowth interface.