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.
While the use of electron probe microanalysis (EPMA) is widespread in the geological and metallurgical sciences, it remains less prevalent in the field of semiconductor research. For these materials, trace element (i.e. dopant) levels typically lie near or beneath the detection limit of wavelength-dispersive Xray (WDX) spectrometers, while alloy compositions of ternary mixtures and multilayer structures can more readily be determined using X-ray diffraction techniques. The electron beam measurements more commonly applied to semiconductors remain transmission electron microscopy (for structural characterization), and scanning electron microscopy (topographic, optical and electrical information).Despite this, there are many aspects of the EPMA that make it an attractive platform for all of these types of semiconductor characterization, particularly when combining compositional information from WDX with complementary and simultaneously-acquired signals. These advantages include: built-in light optics; a stable, quantified and high-current beam; and a combined large-area and high-resolution mapping capability. This allows the measurement of cathodoluminescence (CL), electron beam-induced current (EBIC) and electron channelling contrast imaging (ECCI) signals alongside WDX, which we apply to the investigation of visible and UV Al x In y Ga 1-x-y N materials, devices and nanostructures.Excess charge carriers are fundamental to the function of semiconductor devices, so the ability to directly inject such carriers into a spatially localised region of a sample using an electron beam is invaluable. Optical information comes from the analysis of CL, the light emitted when the carriers recombine radiatively. By measuring in the hyperspectral imaging mode, we observe spatial variations in both emission intensity and wavelength, which correlate with compositional information (e.g. alloy fluctuations) and structural information (e.g. inhomogeneous strain). We extend this technique by looking at the effect on the emission of applying a bias across an electrically contacted sample (e.g. LED) [1]. This more closely matches the CL measurement conditions to those of a working device; at forward bias above the diode threshold this technique converges with electroluminescence (EL), and we now acquire EL hyperspectral images in the EPMA (with the beam off) for direct comparison with CL/WDX data acquired using the same scanning/optics setup. At below-threshold or reverse bias, the device junction can induce a current, resulting in an EBIC signal; as this depends on all recombination pathways, comparison with CL allows the distribution of nonradiative centres to be inferred.Finally, we report recent progress in acquiring structural information using diffraction-based techniques in the EPMA. While the instrument geometry makes the integration of electron backscatter diffraction detectors difficult, we show that useful information on crystal deformation can be obtained using electron channelling contrast imaging (ECCI). This technique use...
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