The use of etched nanorods from a planar template as a growth scaffold for a highly regular GaN/InGaN/GaN core-shell structure is demonstrated. The recovery of m-plane non-polar facets from etched high-aspect-ratio GaN nanorods is studied with and without the introduction of a hydrogen silsesquioxane passivation layer at the bottom of the etched nanorod arrays. This layer successfully prevented c-plane growth between the nanorods, resulting in vertical nanorod sidewalls (∼89.8°) and a more regular height distribution than re-growth on unpassivated nanorods. The height variation on passivated nanorods is solely determined by the uniformity of nanorod diameter, which degrades with increased growth duration. Facet-dependent indium incorporation of GaN/InGaN/GaN core-shell layers regrown onto the etched nanorods is observed by high-resolution cathodoluminescence imaging. Sharp features corresponding to diffracted wave-guide modes in angle-resolved photoluminescence measurements are evidence of the uniformity of the full core-shell structure grown on ordered etched nanorods

III-nitride core-shell nanorods are promising for the development of high efficiency light emitting diodes and novel optical devices. We reveal the nanoscale optical and structural properties of core-shell InGaN nanorods formed by combined top-down etching and regrowth to achieve non-polar sidewalls with a low density of extended defects. While the luminescence is uniform along the non-polar {1–100} sidewalls, nano-cathodoluminescence shows a sharp reduction in the luminescent intensity at the intersection of the non-polar {1–100} facets. The reduction in the luminescent intensity is accompanied by a reduction in the emission energy localised at the apex of the corners. Correlative compositional analysis reveals an increasing indium content towards the corner except at the apex itself. We propose that the observed variations in the structure and chemistry are responsible for the changes in the optical properties at the corners of the nanorods. The insights revealed by nano-cathodoluminescence will aid in the future development of higher efficiency core-shell nanorods

Controlling the long-range homogeneity of core−shell InGaN/GaN layers is essential for their use in light-emitting devices. This paper demonstrates variations in optical emission energy as low as ∼7 meV•μm −1 along the mplane facets from core−shell InGaN/GaN single quantum wells as measured through high-resolution cathodoluminescence hyperspectral imaging. The layers were grown by metal organic vapor phase epitaxy on etched GaN nanorod arrays with a pitch of 2 μm. High-resolution transmission electron microscopy and spatially resolved energy-dispersive X-ray spectroscopy measurements demonstrate a long-range InN-content and thickness homogeneity along the entire 1.2 μm length of the m-plane. Such homogeneous emission was found on the m-plane despite the observation of short-range compositional fluctuations in the InGaN single quantum well. The ability to achieve this uniform optical emission from InGaN/GaN core−shell layers is critical to enable them to compete with and replace conventional planar light-emitting devices.

Abstract. Core-shell indium gallium nitride (InGaN)/gallium nitride (GaN) structures are attractive as light emitters due to the large nonpolar surface of rod-like cores with their longitudinal axis aligned along the c-direction. These facets do not suffer from the quantum-confined Stark effect that limits the thickness of quantum wells and efficiency in conventional light-emitting devices. Understanding InGaN growth on these submicron three-dimensional structures is important to optimize optoelectronic device performance. In this work, the influence of reactor parameters was determined and compared. GaN nanorods (NRs) with both f11-20g a-plane and f10-10g m-plane nonpolar facets were prepared to investigate the impact of metalorganic vapor phase epitaxy reactor parameters on the characteristics of a thick (38 to 85 nm) overgrown InGaN shell. The morphology and optical emission properties of the InGaN layers were investigated by scanning electron microscopy, transmission electron microscopy, and cathodoluminescence hyperspectral imaging. The study reveals that reactor pressure has an important impact on the InN mole fraction on the f10-10g m-plane facets, even at a reduced growth rate. The sample grown at 750°C and 100 mbar had an InN mole fraction of 25% on the f10-10g facets of the NRs. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

GaN/InGaN core−shell nanorods are promising for optoelectronic applications due to the absence of polarization-related electric fields on the sidewalls, a lower defect density, a larger emission volume, and strain relaxation at the free surfaces. The core−shell geometry allows the growth of thicker InGaN shell layers, which would improve the efficiency of light emitting diodes. However, the growth mode of such layers by metal organic vapor phase epitaxy is poorly understood. Through a combination of nanofabrication, epitaxial growth, and detailed characterization, this work reveals an evolution in the growth mode of InGaN epitaxial shells, from a two-dimensional (2D) growth mode to three-dimensional (3D) striated growth without additional line defect formation with increasing layer thickness. Measurements of the indium distribution show fluctuations along the <10−10> directions, with low and high indium composition associated with the 2D and 3D growth modes, respectively. Atomic steps at the GaN/InGaN core−shell interface were observed to occur with a similar frequency as quasi-periodic indium fluctuations along [0001] observed within the 2D layer, to provide evidence that the resulting local strain relief at the steps acts as the trigger for a change of growth mode by elastic relaxation. This study demonstrates that misfit dislocation generation during the growth of wider InGaN shell layers can be avoided by using pre-etched GaN nanorods. Significantly, this enables the growth of absorption-based devices and light-emitting diodes with emissive layers wide enough to mitigate efficiency droop.