Scanning electron microscopy allows for the investigation of materials down to the nanometre scale. In this thesis I combine cathodoluminescence spectroscopy with complementary techniques to investigate a range of III-nitride semiconductor heterostructures. I first describe AlGaN-coreshell nanorod UV-LED structures. Here, I conducted a wideranging study investigating the optical, electrical and structural properties of these structures. The electrical measurements were enabled by a nanoprobing system for in-situ contacting within the scanning electron microscope combined with bespoke focused ion beam deposition and milling to create contacts on individual nanorods. I-V measurements and electron beam induced currents confirmed the formation of a p-n junction and successful doping within the structure. In the same microscope, I measured CL to find the emission properties and found optically active quantum wells emitting near 300nm, with some variation in energy and intensity as well as clustering. In a transmission electron microscope, energy dispersive X-ray analysis confirmed the existence of clusters occurring at a-plane nanofacets. Low temperature and time resolved measurements measure the speed of the recombination in the quantum wells, showing a reduction in the quantum confined Stark effect within these structures. Using this same combination of techniques, I also examined planar UV-LED structures. I found that screw dislocations pinned the position of hexagonal hillocks during growth. In each of the penetrated layers, higher point defect densities and three-dimensional growth enclose the threading dislocations. These point defects can compensate electrical dopants and increase parasitic recombination reducing quantum well emission intensity. I found that during growth, the emergence of multiple facets with distinct incorporation rates leads to alloy composition and doping fluctuations, resulting in hexagonal structures interconnecting and forming a network. I discovered that by changing the alloy compositions present within the LED structure, screwtype threading dislocations can either enhance recombination (non-radiative) or reduced it. Finally I discuss lateral polarity heterostructures, which contain alternating stripes of Gaand N-polar material. Electron backscattered diffraction measurements confirmed the stripes were of the intended polarity but found in addition small inclusions of undesirable material in the Ga-polar regions. With cathodoluminescence spectroscopy I investigated the properties of the two distinct domains as well as their interface. I found that the Ga-polar region displayed far greater defect luminescence, consistent with some previous studies.
| Date of Award | 24 Jun 2022 |
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| Original language | English |
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| Awarding Institution | - University Of Strathclyde
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| Sponsors | University of Strathclyde |
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| Supervisor | Robert Martin (Supervisor) & Paul Edwards (Supervisor) |
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