Cathodoluminescence imaging and spectroscopy of non-polar InGaN quantum wells in core-shell nanostructures



Controlling the long-range homogeneity of core-shell InGaN/GaN layers is essential for their use in light-emitting devices. This dataset contains the results of using high-resolution cathodoluminescence (CL) hyperspectral imaging to measure the homogeneity of the optical emission from single quantum wells formed on the the m-plane facets of core-shell InGaN/GaN nanostructures. The layers were grown by our collaborators at the University of Bath (E. Le Boulbar, I. Girgel, P.-M. Coulon, C. R. Bowen, D. W. E. Allsopp & P. A. Shields) using metal organic vapour phase epitaxy on etched GaN nanorod arrays with a pitch of 2 µm. Three samples were measured, using different growth temperatures for the InGaN layer: 750°C, 650°C and 650°C. The CL results have demonstrated variation in optical emission energy as low as ~7 meV/µm along the facets. The ability to achieve this uniform optical emission from InGaN/GaN core-shell layers is critical in enabling them to compete with and replace conventional planar light-emitting devices.

The CL data presented here consists of subsets of three hyperspectral images, one from each of the 750°C, 650°C and 650°C samples. The measurements were
carried out at room temperature in a modified FEI Quanta 250 field-emission SEM with an accelerating voltage of 5 keV and had a spatial step size of 20 nm. Light was collected using an NA0.28 reflecting objective with its axis perpendicular to the electron beam, and focused directly to the entrance of the spectrograph using an off-axis paraboloidal mirror. We used a 125 mm focal length spectrograph with a 600 lines/mm grating and 50 μm entrance slit, coupled to a cooled electron multiplying charge-coupled device (EMCCD) detector. The CL signal is background-corrected for dark CCD counts. The CL intensity maps are calculated by integrating the signal over the stated energy ranges, giving a signal in units of CCD counts. The spectral data (individual spectra and spectral linescans) is corrected for the non-uniform spectral channel width, giving CL intensity units of counts/eV. Each point in the centroid energy linescans was calculated by averaging over 5 spatial pixels (i.e. 100 nm) in a row perpendicular to the linescan direction.

The paper by E. Le Boulbar et al. (2016) published in Crystal Growth and Design contains additional experimental details, further discussion and complementary results obtained using transmission electron microscopy on the same samples at the Universities of Cambridge and Bristol.
Date made available2016
PublisherUniversity of Strathclyde

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