Evolution of the m-plane Quantum Well Morphology and Composition within a GaN/InGaN Core-Shell Structure

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 benefit 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 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

Structural and optical emission uniformity of m-plane InGaN single quantum wells in 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 m-plane 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

Evolution of the m-plane Quantum Well Morphology and Composition within a GaN/InGaN Core-Shell Structure

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

Insights into Mg²⁺ Intercalation in a Zero-Strain Material: Thiospinel Mg_<i>x</i>Zr₂S₄

The Mg battery cathode material, thiospinel Mg_<i>x</i>Zr₂S₄ (0 ≤ <i>x</i> ≤ 1), exhibits negligible volume change (ca. 0.05%) during electrochemical cycling, providing valuable insight into the limiting factors in divalent cation intercalation. Rietveld refinement of XRD data for Mg_xZr₂S₄ electrodes at various states of charge, , coupled with EDX analysis, demonstrates that Mg²⁺ can be inserted into Zr₂S₄ at 60 °C up to <i>x</i> = 0.7 at a C/10 rate (up to <i>x</i> = 0.9 at very slow rates) and cycled with a high Coulombic efficiency of 99.75%. HAADF-STEM studies provide clear visual evidence of Mg-ion occupation in the lattice, whereas XAS studies show that Zr⁴⁺ was reduced upon Mg²⁺ intercalation. <i>Operando</i> and synchrotron XRD studies reveal the creation of two phases during the latter stages of discharge (<i>x</i> > 0.5) as the lattice fills and Mg²⁺ ions begin occupying tetrahedral (8a) sites in addition to octahedral (16c) interstitial sites. Compared to the isostructural Ti₂S₄ thiospinel, Zr₂S₄ presents a slightly larger cell volume and hence an almost ideal zero-strain lattice on Mg²⁺ insertion. Nonetheless, its 4-fold lower electronic conductivity results in a diffusion coefficient for Mg²⁺ ions (<i>D</i>_Mg; 1 × 10^–10 to 1 × 10^–9 cm²/s) that is more than a factor of 10 lower than in Ti₂S₄. This shows that delocalization of the electron charge carriers in the framework is a very important factor in governing multivalent ion diffusivity in the thiospinel framework and, by extension, in other materials

Investigation of the GaN-on-GaAs interface for vertical power device applications

GaN layers were grown onto (111) GaAs by molecular beam epitaxy. Minimal band offset between the conduction bands for GaN and GaAs materials has been suggested in the literature raising the possibility of using GaN-on-GaAs for vertical power device applications. I-V and C-V measurements of the GaN/GaAs heterostructures however yielded a rectifying junction, even when both sides of the junction were heavily doped with an n-type dopant. Transmission electron microscopy analysis further confirmed the challenge in creating a GaN/GaAs Ohmic interface by showing a large density of dislocations in the GaN layer and suggesting roughening of the GaN/GaAs interface due to etching of the GaAs by the nitrogen plasma, diffusion of nitrogen or melting of Ga into the GaAs substrate

Evolution of the m-plane Quantum Well Morphology and Composition within a GaN/InGaN Core-Shell Structure

This dataset contains the results of scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) Energy Dispersive X-ray (EDX) and Catodoluminescence (CL) measurements carried out on InGaN/GaN core-shell nanostructures. The samples are highly regular arrays of GaN etched cores onto which various InGaN layer thickness were grown using fixed metal organic vapour phase epitaxy (MOVPE) growth conditions. Three different growth time were used to grow InGaN layer with various thickness: 2min, 6min, and 18min, either with or without a GaN capping layer. SEM and AFM characterization techniques were used to assess the nanorod morphology and roughness of the lateral m-plane facets. TEM were used to investigate the structural properties and assess the InGaN thickness of the m-plane facets. EDX measurements were used to assess the InGaN layer composition of the m-plane facet. CL were used to assess the optical properties of each InGaN layer thickness. Correlation of SEM, AFM, TEM, EDX and CL allow to describe the and explain the growth mechanism of a thick InGaN shell grown on GaN NRs formed by combined top-down etching and regrowth

Evolution of the m-plane Quantum Well Morphology and Composition within a GaN/InGaN Core-Shell Structure

This dataset contains the results of scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) Energy Dispersive X-ray (EDX) and Catodoluminescence (CL) measurements carried out on InGaN/GaN core-shell nanostructures. The samples are highly regular arrays of GaN etched cores onto which various InGaN layer thickness were grown using fixed metal organic vapour phase epitaxy (MOVPE) growth conditions. Three different growth time were used to grow InGaN layer with various thickness: 2min, 6min, and 18min, either with or without a GaN capping layer. SEM and AFM characterization techniques were used to assess the nanorod morphology and roughness of the lateral m-plane facets. TEM were used to investigate the structural properties and assess the InGaN thickness of the m-plane facets. EDX measurements were used to assess the InGaN layer composition of the m-plane facet. CL were used to assess the optical properties of each InGaN layer thickness. Correlation of SEM, AFM, TEM, EDX and CL allow to describe the and explain the growth mechanism of a thick InGaN shell grown on GaN NRs formed by combined top-down etching and regrowth

Dataset for Structural and optical emission uniformity of m-plane InGaN single quantum wells in core-shell nanorods

This dataset contains the results of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Energy Dispersive X-ray (EDX) measurements carried out on InGaN/GaN core-shell nanostructures. The samples are highly regular arrays of GaN plasma etched cores onto which wide InGaN layer capped with a GaN layer were grown using different metal organic vapour phase epitaxy (MOVPE) growth parameters. Three different growth temperature were used to grow the InGaN layer: 750°C, 700°C and 650°C. SEM images were used to characterize the describe the fabrication, growth and assess nanorod morphologies. TEM were used to investigate the structural properties and assess the InGaN thickness along the entire length of the m-plane facets. EDX measurements were used to assess the homogeneity of the InGaN layer composition at different position along the m-plane facet and on the semi-polar facets

Evolution of the <i>m</i>‑Plane Quantum Well Morphology and Composition within a GaN/InGaN Core–Shell Structure

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