This dataset provides the experimental data used to generate the figures in the paper entitled "Luminescence behaviour of semi-polar (10-11) InGaN/GaN 'bow-tie' structures on patterned Si substrates".
The room temperature cathodoluminescence (CL) data was recorded using a variable pressure field emission scanning electron microscope (SEM, FEI Quanta 250) which is equipped with a custom-built CL hyperspectral imaging system. The CL system collects the emitted light at an angle of 45° with respect to the incident electron beam using a Cassegrain reflecting objective. The light is then dispersed using a 125 mm focal length spectrograph (Oriel MS125) and detected using an electron-multiplying charge-coupled device (Andor Newton). Low temperature CL was performed in a field emission gun SEM (Zeiss LEO DSM 982) equipped with custom-built liquid helium flow cryostage (CryoVac). The light was collected using a UV-enhanced glass fibre 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-optimised CCD. As the electron beam scans across the sample surface, a whole CL spectrum is recorded per pixel building up the 3D hyperspectral data set. 2D CL images can then be extracted from the hyperspectral data set, such as peak energy, intensity or half width. The room temperature and low temperature (12 K) measurements were acquired with a beam voltage of 5 kV.
Electron channelling contrast imaging is a non-destructive, diffraction technique performed in the SEM. ECC images are generally constructed by measuring the intensity of the backscattered electrons (BSEs) as the electron beam scans across the surface of a suitably-orientated sample. Any changes in crystallographic orientation and local strain can be monitored by the variation in the BSE intensity causing a change in contrast in an ECC image. This allows the imaging of low-angle tilt and rotation boundaries, atomic steps and extended defects (e.g. TDs). ECCI is carried out in a forward scattering geometry in a field emission SEM (FEI Sirion 200), equipped with an electron-sensitive diode and a custom-built signal amplifier.
Electron backscatter diffraction (EBSD) measurements were performed using a Nordlys EBSD detector from Oxford Instruments attached to an FEI Quanta 250 variable pressure field emission SEM. The EBSD data was acquired at 20 kV and at a sample tilt of 70° with respect to the normal of the incident electron beam. For the analysis of the EBSD data, the electron backscatter pattern (EBSP) from each pixel was compared to simulated dynamical Kikuchi patterns using a Bloch wave approach.
Abstract of the paper:
In this work, we report on the innovative growth of semi-polar 'bow-tie'-shaped GaN structures containing InGaN/GaN multiple quantum wells (MQWs), and on their structural and luminescence characterisation. 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 channelling contrast imaging (ECCI) identifies the black spots as threading dislocations (TDs) 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 centre 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.