A5025290498- GaN-based semiconductor devices and materials
- Semiconductor Quantum Structures and Devices
- Photonic and Optical Devices
- Semiconductor materials and devices
- Photonic Crystals and Applications
- Metal and Thin Film Mechanics
- ZnO doping and properties
- Optical Coatings and Gratings
- Ga2O3 and related materials
- Semiconductor Lasers and Optical Devices
- Quantum and electron transport phenomena
- Acoustic Wave Resonator Technologies
- Spectroscopy and Quantum Chemical Studies
- Advancements in Semiconductor Devices and Circuit Design
- TiO2 Photocatalysis and Solar Cells
- Semiconductor materials and interfaces
- Integrated Circuits and Semiconductor Failure Analysis
- Anodic Oxide Films and Nanostructures
- Optical Network Technologies
- Nanowire Synthesis and Applications
- Gas Sensing Nanomaterials and Sensors
- Advanced Semiconductor Detectors and Materials
- Nanofabrication and Lithography Techniques
- Advanced Photocatalysis Techniques
- Spectroscopy and Laser Applications
University of Bath
2011-2020
University of Cambridge
2014
University of Strathclyde
2014
Universities UK
1988-2003
University of York
1989-2002
York University
1994
BT Group (United Kingdom)
1987
University of Manchester
1982-1986
University of Sheffield
1976
Subwavelength scale antireflection moth-eye structures in silicon were fabricated by a wafer-scale nanoimprint technique and demonstrated an average reflection of 1% the spectral range from 400 to 1000 nm at normal incidence. An excellent property out large incident angles is shown with below 8% 60°. Pyramid array gave almost constant about 10% for angle up 45° concave-wall column produced approximately linear relation between angles. The promising improving conversion efficiencies solar cells.
Ultraviolet light emitting diodes (UV-LEDs) are attracting the interest of researchers for design compact photoreactors due to their energy efficiency, life expectancy, flexibility, and easily tuned intensity emission wavelength. However, quasi-point source nature viewing angle dependence these illumination sources, distribution in LED based reactors can be highly inhomogeneous if locations LEDs reactor not carefully designed. This work describes a novel standardized accurate measurements...
The impact of trench defects in blue InGaN/GaN light emitting diodes (LEDs) has been investigated. Two mechanisms responsible for the structural degradation multiple quantum well (MQW) active region were identified. It was found that during growth p-type GaN capping layer, loss part enclosed within a defect occurred, affecting top-most QWs MQW stack. Indium platelets and voids also to form preferentially at bottom presence high densities LEDs relate significant reduction photoluminescence...
Top-down fabricated GaN nanowires, 250 nm in diameter and with various heights, have been used to experimentally determine the evolution of strain along vertical direction 1-dimensional objects. X-ray diffraction photoluminescence techniques obtain profile inside nanowires from their base top facet for both initial compressive tensile strains. The relaxation behaviors derived optical structural characterizations perfectly match numerical results calculations based on a continuous media...
Abstract Hyperspectral cathodoluminescence imaging provides spectrally and spatially resolved information on luminescent materials within a single dataset. Pushing the technique toward its ultimate nanoscale spatial limit, while at same time dispersing collected light before detection, increases challenge of generating low-noise images. This article describes aspects instrumentation, in particular data treatment methods, which address this problem. The methods are demonstrated by applying...
Photoluminescence and electroluminescence measurements on InGaN/GaN quantum well (QW) structures light emitting diodes suggest that QWs with gross fluctuations in width (formed when, during growth, the InGaN is exposed unprotected to high temperatures) give higher room temperature efficiencies than continuous QWs. The efficiency does not depend growth of GaN barriers. Temperature-dependent results from activation energies for defect-related non-radiative recombination QW samples gaps. At...
The use of etched nanorods from a planar template as growth scaffold for highly regular GaN/InGaN/GaN core-shell structure is demonstrated. recovery m-plane non-polar facets high-aspect-ratio GaN studied with and without the introduction hydrogen silsesquioxane passivation layer at bottom nanorod arrays. This successfully prevented c-plane between nanorods, resulting in vertical sidewalls (∼89.8°) more height distribution than re-growth on unpassivated nanorods. variation passivated solely...
High-aspect-ratio GaN-based nanostructures are of interest for advanced photonic crystal and core-shell devices. Nanostructures grown by a bottom-up approach limited in terms doping, geometry shape which narrow their potential application areas. In contrast, high uniformity greater diversity design can be produced via top-down etching approach. However, detailed understanding the role etch process parameters is lacking creating high-aspect ratio nanorods nanopores. Here we report systematic...
The efficiency of light emitting diodes (LEDs) remains a topic great contemporary interest due to their potential reduce the amount energy consumed in lighting. current consensus is that electrons and holes distribute themselves through emissive region by drift-diffusion process which results highly non-uniform distribution emission can efficiency. In this paper, measured variations external quantum range InGaN/GaN LEDs with different numbers wells (QWs) are shown compare closely predictions...
Controlling the long-range homogeneity of core–shell InGaN/GaN layers is essential for their use in light-emitting devices. This paper demonstrates variations optical emission energy as low ∼7 meV·μm–1 along m-plane facets from single quantum wells measured through high-resolution cathodoluminescence hyperspectral imaging. The were grown by metal organic vapor phase epitaxy on etched GaN nanorod arrays with a pitch 2 μm. High-resolution transmission electron microscopy and spatially resolved...
Abstract Gallium nitride nanorod arrays have been created via dry etching in Cl 2 /Ar plasma using a Ni mask formed by nanoimprint lithography and lift‐off. Aspect ratios greater than 20 are demonstrated optimizing the etch conditions to achieve near‐vertical sidewalls. Such top‐down etched uniformity when compared bottom‐up arrays, with process already having on 4‐inch wafers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
III-nitride core-shell nanorods are promising for the development of high efficiency light emitting diodes and novel optical devices. We reveal nanoscale structural properties InGaN formed by combined top-down etching regrowth to achieve non-polar sidewalls with a low density extended defects. While luminescence is uniform along {1–100} sidewalls, nano-cathodoluminescence shows sharp reduction in luminescent intensity at intersection facets. The accompanied emission energy localised apex...
InxGa1-xN/GaN quantum wells have been grown on the {1011} facets of dense arrays self-assembled GaN nano-pyramids formed by selective area growth and characterised high spatial resolution cathodoluminescence. The pyramids are shown to significantly reduced defect (green-yellow) band emission well luminescence is correspondingly intense. peak energy this blue-shift as sampled region moved up pyramid facets, revealing that InN incorporation in such closely spaced epitaxial nanostructures...
We report the ability to control relative InN incorporation in InGaN/GaN quantum wells (QWs) grown on semi-polar and non-polar facets of a core-shell nanorod LED structure by varying growth conditions. A study cathodoluminescence emitted from series structures with different temperatures pressures for InGaN QW layer revealed that increasing pressure had effect facets, while temperature improves uniformity light emission QWs facets.
Core–shell indium gallium nitride (InGaN)/gallium (GaN) structures are attractive as light emitters due to the large nonpolar surface of rod-like cores with their longitudinal axis aligned along c-direction. These facets do not suffer from quantum-confined Stark effect that limits thickness quantum wells and efficiency in conventional light-emitting devices. Understanding InGaN growth on these submicron three-dimensional is important optimize optoelectronic device performance. In this work,...
Abstract TiO 2 nano‐tubes have been generated by anodising commercially pure (99.6%) titanium in a 1 M solution of Na SO 4 which contains small amount NaF (0.1–1 wt%). The use an initial voltage ramp, prior to the application constant cell, led increase thickness nano‐tube layer. thermal stability layer has also evaluated annealing at variety temperatures, from 200 600 °C. Scanning Electron Microscopy (SEM) annealed indicate that they are stable up 500 Raman spectroscopy was performed...
Composite silicon–polycrystalline chemical vapour deposition (CVD) diamond wafers are potential substrates for GaN-based devices use in harsh environments due to their high thermal conductivity and stability. When cooled from a typical temperature of approximately 800 25 °C wafer bowing arises mismatch the coefficients expansion silicon polycrystalline diamond. In this paper 100 mm diameter have been modelled using ANSYS finite element software investigate behaviour as function geometry. The...
Microcavities based on group-III nitride material offer a notable platform for the investigation of light-matter interactions as well development devices such high efficiency light emitting diodes (LEDs) and low-threshold nanolasers.Disk or tube geometries in particular are attractive lasing applications due to their ability support finesse whispering gallery modes (WGMs) small modal volumes.In this article we present fabrication homogenous dense arrays axial InGaN/GaN nanotubes via...
The far-field profile of photonic quasi-crystal patterned and unpatterned LEDs, fabricated from commercial epitaxial substrates by electron beam lithography, has been measured prior to lapping dicing. Emission enhancements reach a maximum 62%, are strongly dependent on the filling factor. Qualitative agreement is achieved between 2-D finite-difference time-domain calculations experimental data.