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Title: III-Nitride : fabrication and characterisation of micron and sub-micron structured electrically injected light-emitting diode
Author: Ghataora, Suneal S.
ISNI:       0000 0004 8506 3202
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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This thesis is focused toward the fabrication and characterisation of electrically injected micron and sub-micron featured III-nitride light-emitting diode (LED), demonstrating new and interesting device structures. A number of unique fabrication process have been developed in the production of 2D micro-hole array, 1D nano-grating array and single micro/nano-pillar structured light-emitting devices. Initial efforts consider the combined complimentary benefits of the organic and inorganic semiconductor material systems, featuring the respective highperformance fluorescent quantum yield and electrical properties. The main advantage to a hybrid organic/inorganic LED is the highly-efficient radiation-less Förster resonance energy transfer (FRET) process, requiring near-field proximity (< 10 nm) between donor (InGaN/GaN MQW) and acceptor (organic light-emitting polymer) dipole. A 2D micro-hole and 1D nano-grating array structure through the InGaN/GaN MQW of a high-performance LED have both been demonstrated to provide the necessary dipole-dipole separation; resulting in respective FRET efficiencies of 16.7 % and 31.3 %, where total FRET interaction area accounts just 0.64 % and 3.91 % The emission of a c-plane III-nitride LED is intrinsically unpolarised, periodic 1D nano-grating arrays mean it can serve as an efficient blue light-emitter and polariser through anisotropic strain relaxation. A uniaxial alignment of the otherwise highly-disordered organic molecules is also then achieved through effective nanoconfinement to the 1D nano-grating structure, substantially increasing polarised light absorption/emission with the molecular order. The polarisation dependent measurements show the hybrid organic/inorganic device with a combined white light polarisation degree up to 44 %; electrically injected blue emitting devices have a highest 34 % polarisation degree with largest nano-grating duty-cycle. A novel sub-wavelength fabrication method is also documented with the development and optimisation of a modified single-instrument direct-write laser photolithography and high-resolution confocal photoluminescence microscopy system; demonstrating mask-less laser-ablation and exposure of photoresist below diffraction-limited spot-size. In a technical demonstration the electrical characteristics of a 3.7 μm and 13 μm diameter single micro-pillar structured III-nitride LED are presented, but more significantly single nano-pillar devices with respective 326.2 nm and 382.1 nm diameter are also shown.
Supervisor: Wang, Tao ; Smith, Richard M. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available