Abstract: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… Show more
“…. But within a nanorod geometry, up to four different facets can co‐exist, so that competition between various growth directions occurs. In this study, we have demonstrated that the change in V/III ratio has a major impact on the AlN regrowth along <0001>, <10‐10>, and <11‐20>.…”
Core–shell nanostructures are predicted to highly improve the efficiency of deep‐UV light emitting diodes (LEDs), owing to their low defect density, reduced quantum‐confined Stark effect, high‐quality non‐polar growth and improved extraction efficiency. In this paper, we report on the nanofabrication of high‐quality AlN nanorod arrays using a hybrid top‐down/bottom‐up approach for use as a scaffold for UV LED structures. We describe the use of Displacement Talbot Lithography to fabricate a metallic hard etch mask to allow AlN nanorod arrays to be dry etched from a planar AlN template. In particular, we investigate the impact of etching parameters on the nanorod etch rate, tapering profile and mask selectivity in order to achieve vertical‐sided nanorod arrays with high aspect ratios. AlN facet recovery is subsequently explored by means of regrowth using Metal Organic Vapor Phase Epitaxy. Low pressure and high V/III ratio promote straight and smooth sidewall faceting, which results in an improvement of the optical quality compared to the initial AlN template. The promising results open new perspectives for the fabrication of high‐efficiency deep‐UV‐emitting core–shell LEDs.
“…. But within a nanorod geometry, up to four different facets can co‐exist, so that competition between various growth directions occurs. In this study, we have demonstrated that the change in V/III ratio has a major impact on the AlN regrowth along <0001>, <10‐10>, and <11‐20>.…”
Core–shell nanostructures are predicted to highly improve the efficiency of deep‐UV light emitting diodes (LEDs), owing to their low defect density, reduced quantum‐confined Stark effect, high‐quality non‐polar growth and improved extraction efficiency. In this paper, we report on the nanofabrication of high‐quality AlN nanorod arrays using a hybrid top‐down/bottom‐up approach for use as a scaffold for UV LED structures. We describe the use of Displacement Talbot Lithography to fabricate a metallic hard etch mask to allow AlN nanorod arrays to be dry etched from a planar AlN template. In particular, we investigate the impact of etching parameters on the nanorod etch rate, tapering profile and mask selectivity in order to achieve vertical‐sided nanorod arrays with high aspect ratios. AlN facet recovery is subsequently explored by means of regrowth using Metal Organic Vapor Phase Epitaxy. Low pressure and high V/III ratio promote straight and smooth sidewall faceting, which results in an improvement of the optical quality compared to the initial AlN template. The promising results open new perspectives for the fabrication of high‐efficiency deep‐UV‐emitting core–shell LEDs.
“…The emission spectra from each of the facets are relative to the nonpolar facet and reveals that the peak emission is more than an order of magnitude more intense than from the other facets and dominates the nanorod emission. The brighter intensity from the non-polar sidewalls may arise from the mitigation of the internal electric fields leading to stronger overlap of the electron and hole wavefunctions as well as from the optimised growth parameters 25 . The lowest energy emission, at a peak energy 2.48 eV, arises from the polar tips of the nanorods, whilst there is an increase in the peak energy of the emission from the semipolar facets to 2.53 eV.…”
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
“…1c prism(1)) is in the base of the nanorod, where only the GaN near band edge (NBE) signal can be detected, showing that no In x Ga 1− x N growth occurred on the m -plane sidewalls during the deposition of the InGaN/GaN active zone. This is expected given the ultradense nature of the array 10 from which the individual rod was extracted and in contrast to nanorods with a wider spacing where In x Ga 1− x N growth could be found on the m -plane 12 , 13 . The small FWHM (113 meV at 300 K) of the GaN NBE peak and the absence of any yellow luminescence on the m -plane sidewalls indicate that damage introduced during the etching process was successfully healed during the regrowth and the material is of high optical quality 14 – 17 .…”
Section: Resultsmentioning
confidence: 99%
“…2a ). This is most likely caused by the extinction of a -plane facets during the regrowth 13 , 18 . Figure 2 Intensity plots of the emission GaN NBE emission ( a ), the semipolar QW emission between 395 nm and 480 nm ( b ), and the emission observed from the apex of the nanorod from 490 nm to 650 nm ( c ).…”
Multiple luminescence peaks emitted by a single InGaN/GaN quantum-well(QW) nanorod, extending from the blue to the red, were analysed by a combination of electron microscope based imaging techniques. Utilizing the capability of cathodoluminescence hyperspectral imaging it was possible to investigate spatial variations in the luminescence properties on a nanoscale. The high optical quality of a single GaN nanorod was demonstrated, evidenced by a narrow band-edge peak and the absence of any luminescence associated with the yellow defect band. Additionally two spatially confined broad luminescence bands were observed, consisting of multiple peaks ranging from 395 nm to 480 nm and 490 nm to 650 nm. The lower energy band originates from broad c-plane QWs located at the apex of the nanorod and the higher energy band from the semipolar QWs on the pyramidal nanorod tip. Comparing the experimentally observed peak positions with peak positions obtained from plane wave modelling and 3D finite difference time domain(FDTD) modelling shows modulation of the nanorod luminescence by cavity modes. By studying the influence of these modes we demonstrate that this can be exploited as an additional parameter in engineering the emission profile of LEDs.
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