A5080710577- GaN-based semiconductor devices and materials
- Semiconductor Quantum Structures and Devices
- Ga2O3 and related materials
- ZnO doping and properties
- Semiconductor materials and devices
- Metal and Thin Film Mechanics
- Chalcogenide Semiconductor Thin Films
- Quantum Dots Synthesis And Properties
- Advanced Semiconductor Detectors and Materials
- Semiconductor materials and interfaces
- Acoustic Wave Resonator Technologies
- Electron and X-Ray Spectroscopy Techniques
- Semiconductor Lasers and Optical Devices
- Nanowire Synthesis and Applications
- Optical Coatings and Gratings
- Photocathodes and Microchannel Plates
- Gold and Silver Nanoparticles Synthesis and Applications
- Quantum and electron transport phenomena
- Thin-Film Transistor Technologies
- Photonic and Optical Devices
- Silicon Carbide Semiconductor Technologies
- Plasma Diagnostics and Applications
- Ion-surface interactions and analysis
- Plasmonic and Surface Plasmon Research
- Advanced Electron Microscopy Techniques and Applications
University College Cork
2014-2024
Tyndall Centre
2015-2023
National University of Ireland
2014-2020
International Energy Research Centre
2012-2020
Tyndall National Institute
2012-2015
University of Sheffield
2002-2012
University of Strathclyde
1990-2012
University of Glasgow
2012
University of Liverpool
2012
Engineering and Physical Sciences Research Council
2000-2010
Solid state UV emitters have many advantages over conventional sources. The (Al,In,Ga)N material system is best suited to produce LEDs and laser diodes from 400 nm down 210 nm—due its large tuneable direct band gap, n- p-doping capability up the largest bandgap AlN a growth fabrication technology compatible with current visible InGaN-based LED production. However AlGaN based UV-emitters still suffer numerous challenges compared their counterparts that become most obvious by consideration of...
Abstract Typical light‐emitting diodes (LEDs) have a form factor >(300 × 300) µm 2 . Such LEDs are commercially mature in illumination and ultralarge displays. However, recent LED research includes shrinking individual sizes from side lengths >300 to values <100 µm, leading devices called micro‐LEDs. Their advent creates number of exciting new application spaces. Here, review the principles applications micro‐LED technology is presented. In particular, implications reduced size...
An organic passivation process for nitride nanowires was first proposed to reduce Shockley–Read–Hall non-radiative recombination of nanowire light emitting diodes.
The gate leakage behavior in AlGaN/GaN heterostructure field-effect transistors was studied as a function of applied bias, temperature, and surface periphery. A hopping conduction mechanism with an activation energy 0.21 eV is proposed for the gate–drain voltages that exceed pinchoff. reverse breakdown voltage device exhibited negative temperature coefficient −0.11 V K−1, suggesting other than impact ionization, such thermal runaway, may be responsible.
The valence band offset of wurtzite-InN∕AlN (0001) heterojunctions is determined by x-ray photoelectron spectroscopy to be 1.52±0.17eV. Together with the resulting conduction 4.0±0.2eV, a type-I heterojunction forms between InN and AlN in straddling arrangement.
We report an inexpensive nanoscale patterning process for epitaxial lateral overgrowth (ELOG) in AlN layers grown by metal organic vapour phase epitaxy (MOVPE) on sapphire.
We describe the use of electron channeling contrast imaging in scanning microscope to rapidly and reliably image identify threading dislocations (TDs) materials with wurtzite crystal structure. In imaging, vertical TDs are revealed as spots black-white contrast. have developed a simple geometric procedure which exploits differences observed direction this for screw, edge, mixed two images acquired from symmetrically equivalent planes whose $\mathbit{g}$ vectors at...
Bulk gallium nitride (GaN) power semiconductor devices are gaining significant interest in recent years, creating the need for technology computer aided design (TCAD) simulation to accurately model and optimize these devices. This paper comprehensively reviews compares different GaN physical models parameters literature, discusses appropriate selection of TCAD simulation. 2-D drift-diffusion semi-classical is carried out 2.6 kV 3.7 bulk vertical PN diodes. The simulated forward...
In this paper we describe the use of electron backscatter diffraction (EBSD) mapping and channeling contrast imaging---in scanning microscope---to study tilt, atomic steps dislocations in epitaxial $\mathrm{GaN}$ thin films. We show results from a series films increasing thickness just coalesced laterally overgrown film. From our deduce that EBSD may be used to measure orientation changes order 0.02\ifmmode^\circ\else\textdegree\fi{}, As has spatial resolution...
We report on the electrical-to-optical modulation bandwidths of non-mesa-etched semipolar (112¯2) InGaN/GaN light-emitting diodes (LEDs) operating at 430–450 nm grown high-quality GaN templates, which were prepared patterned (101¯2) r-plane sapphire substrates. The measured frequency response −3 dB LEDs was up to 1 GHz. A high back-to-back data transmission rate above 2.4 Gbps is demonstrated using a non-return-to-zero on-off keying scheme. This indicates that are suitable gigabit per second...
The limited modulation bandwidth of commercial light-emitting diodes (LEDs) is one the critical bottlenecks for visible light communications. Possible approaches to increase include use micron sized LEDs, which can withstand higher current densities, as well LED structures that are grown on different crystal planes conventional polar c-plane. We compare c-plane InGaN/GaN LEDs with semipolar (112̅2) containing a 4- and 8-nm single quantum well. active areas varying from 200 × 30 μm <sup...
Abstract Polarisation doping of Al x Ga 1− N, through grading , has realised major improvements in p -type conductivity ultraviolet (UV) light-emitting diodes (LEDs) compared to conventional impurity doping. However, the exact balance between two regimes achieve best device performance is not clear, especially as a function operating wavelength. In this work, 330 nm LEDs with varied -doping approaches were characterised temperature: Mg doped only (reference); polarisation and (co-doped);...
Polarisation doping of Al$_x$Ga$_{1-x}$N, through grading $x$, has realised major improvements in $p$-type conductivity ultraviolet (UV) light-emitting diodes (LEDs) compared to conventional impurity doping. However, the exact balance between two regimes achieve best device performance is not clear, especially as a function operating wavelength. In this work, 330 nm LEDs with varied $p$-doping approaches were characterised temperature: Mg doped only (reference); polarisation and (co-doped);...
Despite considerable advancements, high electron mobility transistors (HEMTs) based on gallium nitride (GaN) channels remain largely limited to power applications below 650 V. For higher demands, the ultra-wide bandgap semiconductor alloy aluminium nitride, (Al,Ga)N, has emerged as a key contender for next-generation HEMTs. In this theoretical study, we show that Al-rich Al$_x$Ga$_{1-x}$N-channel HEMTs (with $x \geq 0.5$) outperform GaN-channel counterparts at and above room temperature,...
Different dielectrics were used for post-processing surface passivation of AlGaN/GaN heterostructure field-effect transistors (HFETs) and the resulting electrical characteristics examined. An increase in maximum drain current approximately 25% was observed after Si3N4 SiO2 deposition ~15% annealed SiO on HFETs. In all cases, found to gate leakage with an reduction activation energy. However, rise least SiO. The plasma enhanced chemical vapour method not contribute mechanism, whilst presence...
We report a study of the morphology and composition InxGa1−xN/GaN multiple-quantum-well structures their sensitivity to electron-beam damage. have employed high-resolution transmission electron microscopy, energy dispersive x-ray analysis, scanning microscopy. Microstructural analysis was performed investigate dynamical effects irradiation on relative indium distribution within quantum wells. Exposure relatively low incident beam illumination, corresponding current densities at specimen ∼100...
A combined experimental and theoretical study is presented of the band gap AlInN, confirming breakdown virtual crystal approximation (VCA) for conduction valence edges. Composition dependent bowing parameters these quantities are extracted. Additionally, composition offsets GaN/AlInN systems provided. We show that local strain built-in fields affect edges significantly, leading to optical polarization switching at much lower In than expected from a VCA approach.
Reflection anisotropy spectroscopy (RAS) and reflection high-energy electron diffraction (RHEED) were applied to study clean InP(001) surfaces prepared by molecular beam epitaxy (MBE). At phosphorus equivalent pressures (BEPs) between 3.5×10−7 3.5×10−6 mbar substrate temperature (Ts) falling from 590 150 °C, (2×4), (2×1), (2×2), c(4×4) RHEED patterns are observed. The main RAS features, observed at 1.7–1.9 2.6–2.9 eV assigned In P dimers, respectively. above reconstruction sequence is...
The high-pressure wurtzite to rocksalt phase transition of high quality epitaxial GaN has been studied using Raman scattering and optical absorption spectroscopy. results are compared with ab initio calculations performed within the framework density functional theory. due phonon modes was followed up $69\phantom{\rule{0.3em}{0ex}}\text{GPa}$; marked by appearance new features which we assign disorder activated, symmetry forbidden, from phase. There is no evidence for recently proposed...