Three-dimensional cathodoluminescence characterization of a semipolar GaInN based LED sample

Journal of Applied Physics

Gong

et al. 2018

This version is available at https://strathprints.strath.ac.uk/63662/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output. Epitaxial overgrowth of semi-polar III-nitride layers and devices often leads to arrowhead-shaped surface features, referred to as chevrons. We report on a study into the optical, structural, and electrical properties of these features occurring in two very different semi-polar structures, a blueemitting multiple quantum well structure, and an amber-emitting light-emitting diode. Cathodoluminescence (CL) hyperspectral imaging has highlighted shifts in their emission energy, occurring in the region of the chevron. These variations are due to different semi-polar planes introduced in the chevron arms resulting in a lack of uniformity in the InN incorporation across samples, and the disruption of the structure which could cause a narrowing of the quantum wells (QWs) in this region. Atomic force microscopy has revealed that chevrons can penetrate over 150 nm into the sample and quench light emission from the active layers. The dominance of non-radiative recombination in the chevron region was exposed by simultaneous measurement of CL and the electron beam-induced current. Overall, these results provide an overview of the nature and impact of chevrons on the luminescence of semi-polar devices.

Section: Resultssupporting

confidence: 74%

Cathodoluminescence studies of chevron features in semi-polar (112¯2) InGaN/GaN multiple quantum well structures

Brasser

Journal of Applied Physics

Gong

et al. 2018

“…CL is a useful tool to spatially resolve their luminescence and investigate the incorporation of AlN around their different facets as discussed in the following paragraphs 31 . Chevrons are also observed in semi-polar InGaN/GaN QW structures and LEDs emitting in the visible region and CL imaging showed the direct influence on the light emission 32 , 33 . As shown later, the tips of the chevrons are aligned along the -direction.…”

Section: Resultsmentioning

confidence: 99%

Spatially-resolved optical and structural properties of semi-polar $$\mathrm{(11}\bar{2}\mathrm{2)}$$ Al x Ga1−x N with x up to 0.56

Naresh-Kumar

et al. 2017

Sci Rep

Pushing the emission wavelength of efficient ultraviolet (UV) emitters further into the deep-UV requires material with high crystal quality, while also reducing the detrimental effects of built-in electric fields. Crack-free semi-polar AlxGa1−xN epilayers with AlN contents up to x = 0.56 and high crystal quality were achieved using an overgrowth method employing GaN microrods on m-sapphire. Two dominant emission peaks were identified using cathodoluminescence hyperspectral imaging. The longer wavelength peak originates near and around chevron-shaped features, whose density is greatly increased for higher contents. The emission from the majority of the surface is dominated by the shorter wavelength peak, influenced by the presence of basal-plane stacking faults (BSFs). Due to the overgrowth technique BSFs are bunched up in parallel stripes where the lower wavelength peak is broadened and hence appears slightly redshifted compared with the higher quality regions in-between. Additionally, the density of threading dislocations in these region is one order of magnitude lower compared with areas affected by BSFs as ascertained by electron channelling contrast imaging. Overall, the luminescence properties of semi-polar AlGaN epilayers are strongly influenced by the overgrowth method, which shows that reducing the density of extended defects improves the optical performance of high AlN content AlGaN structures.

“…The light was collected using a UV-enhanced glass fiber placed in close contact with the sample, dispersed with a 90 cm focal length monochromator (SPEX 1702), and detected using a liquid nitrogen-cooled, UV-optimized CCD. 18 In both microscopes, the CL was collected in hyperspectral imaging mode, where a spectrally-resolved luminescence spectrum is collected for every pixel in the image. The room temperature and low temperature (%12 K) measurements were acquired with a beam voltage of 5 kV.…”

Section: Methodsmentioning

confidence: 99%

Luminescence behavior of semipolar (101¯1) InGaN/GaN “bow-tie” structures on patterned Si substrates

Journal of Applied Physics

Trager-Cowan

Hourahine

et al. 2020

Self Cite

In this work, we report on the innovative growth of semipolar "bow-tie"-shaped GaN structures containing InGaN/GaN multiple quantum wells (MQWs) and their structural and luminescence characterization. We investigate the impact of growth on patterned (113) Si substrates, which results in the bow-tie cross section with upper surfaces having the (10 11) orientation. Room temperature cathodoluminescence (CL) hyperspectral imaging reveals two types of extended defects: black spots appearing in intensity images of the GaN near band edge emission and dark lines running parallel in the direction of the Si stripes in MQW intensity images. Electron channeling contrast imaging (ECCI) identifies the black spots as threading dislocations propagating to the inclined (10 11) surfaces. Line defects in ECCI, propagating in the [1 210] direction parallel to the Si stripes, are attributed to misfit dislocations (MDs) introduced by glide in the basal (0001) planes at the interfaces of the MQW structure. Identification of these line defects as MDs within the MQWs is only possible because they are revealed as dark lines in the MQW CL intensity images, but not in the GaN intensity images. Low temperature CL spectra exhibit additional emission lines at energies below the GaN bound exciton emission line. These emission lines only appear at the edge or the center of the structures where two (0001) growth fronts meet and coalesce (join of the bow-tie). They are most likely related to basal-plane or prismatic stacking faults or partial dislocations at the GaN/Si interface and the coalescence region.