Cathodoluminescence spectra and images acquired from site-controlled InGaN quantum discs

Abstract

This data is the result of measuring cathodoluminescence (CL) from site-controlled InGaN quantum discs grown on ultra-high density GaN nanorod array templates. The samples were grown using metal organic chemical vapour deposition (MOCVD) by collaborators at the Tyndall National Institute and University College Cork. This method of growth is intended to improve the light-emitting performance of the material through a reduction in both the elastic strain and the density of crystallographic defects. The CL measurements whose results are presented here were carried out in order to demonstrate these improvements on the required sub-micrometre length scale. Comparison of this data has also been made with the results of two techniques carried out at other insitutions: transmission electron microscopy (STEM) and energy-dispersive X-ray (EDX) mapping. This additional data is not published here, but can be seen along with the CL data in the paper by Conroy et al., (2016) Nanoscale vol. 8 p. 11019 (DOI: 10.1039/c6nr00116e). For simplicity, the filenames of the CL data presented here correspond to the Figure numbers in this paper. Room temperature CL hyperspectral imaging was conducted in a scanning electron microscope (FEI Quanta 250) using a 5 kV, ~5 nA beam. The samples were tilted by 45° with respect to the incident electron beam and the generated light collected by a reflecting objective with its optical axis perpendicular to the electron beam. The light was dispersed with with a 125 mm focal length spectrograph equipped with with a 50 µm slit and a 600 lines/mm grating blazed at 200 nm, and detected using a cooled 1600-channel electron-multiplying charge coupled device (reduced to 800 channels by 2× binning) with an acquisition time of 200 ms/spectrum. All the data shown is extracted from these hyperspectral images, and is background corrected by subtracting a dark spectrum. The first CL hyperspectral image was acquired over a 5×5 µm area of the sample using a scan step of 50 nm. Fig3a-spectrum.txt and Fig3b-spectrum.txt show CL spectra emitted from a nanorod sidewall and nanorod tip respectively. CL intensity images were extracted from the same hyperspectral dataset using the energy ranges 2.65-3.70 eV (Fig3a-image.txt) and 1.88-2.50 eV (Fig3b-image.txt). A second CL hyperspectral image was acquired over a single nanorod, using 20 nm steps to scan over an area of 2×2 µm. Intensity images were extracted from this using the energy ranges 3.20-3.50 eV (Fig4c-image1.txt), 2.65-3.15 eV (Fig4c-image2.txt) and 1.88-2.50 eV (Fig4c-image3.txt). A spectral linescan (Fig4b-linescan.txt) shows the variation in emission spectrum as a function of distance from the base to apex of the nanorod. This data is given in units of counts/eV, using equal energy divisions from 1.882 eV to 3.736 eV (left-right in data array) and with a total linescan length of 1.41 µm (bottom-top of data array corresponding to base-apex of nanorod). Finally, the chromaticity information (calculated using CIE 1931 colour space) is given in Fig4a-colour.txt; this chromaticity data is indicative only, as no correction has been made for the the spectral response of the system.