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Ternary III-nitride-based nanowires with highly efficient light-emitting properties are essential for a broad range of applications. By using the selective area molecular-beam epitaxy method, InGaN/AlGaN quantum disks (QDs) embedded in hexagonal GaN nanowires were successfully grown. With the help of atomic-scale-resolved transmission electron microscopy and atom probe tomography, atomic ordering and other related structural information, such as crystallography and local chemistry, have been unambiguously revealed to provide unique insights into the exceptionally strong photoluminescence enhancements. A boomerang-shaped InGaN/AlGaN QD was identified, and atomic-level 1 : 1 periodic chemical ordering within the boomerang shaped AlGaN layers along the c -direction was revealed, confirming the preferential site occupation of Al-atoms. This type of growth provides a strong suppression of the quantum-confined Stark effect and is thus likely a very strong contributor to the exceptional properties. This work therefore enables us to directly establish the key structural elements necessary to understand the exceptionally strong emission exhibited by these materials. Optimization of the configurations of QDs could be an alternative design tool for developing various advanced LED device applications with well-designed structure and desirable optical properties. 

Due to the increasing desire for nanoscale optoelectronic devices with green light emission capability and high efficiency, ternary III‐N‐based nanorods are extensively studied. Many efforts have been taken on the planar device configuration, which lead to unavoided defects and strains. With selective‐area molecular‐beam epitaxy, new “Russian Doll”‐type InGaN/AlGaN quantum wells (QWs) have been developed, which could largely alleviate this issue. This work combines multiple nanoscale characterization methods and k∙p theory calculations so that the crystalline structure, chemical compositions, strain effects, and light emission properties can be quantitatively correlated and understood. The 3D structure and atomic composition of these QWs are retrieved with transmission electron microscopy and atom probe tomography while their green light emission has been demonstrated with room‐temperature cathodoluminescence experiments. k∙p theory calculations, with the consideration of strain effects, are used to derive the light emission characteristics that are compared with the local measurements. Thus, the structural properties of the newly designed nanorods are quantitatively characterized and the relationship with their outstanding optical properties is described. This combined approach provides an innovative way for analyzing nano‐optical‐devices and new strategies for the structure design of light‐emitting diodes.