Publications

Corrigendum : Cathodoluminescence nano-characterization of semiconductors (2011 Semicond. Sci. Technol. 26 064005)

Edwards Paul R, Martin Robert W

Semiconductor Science and Technology Vol 33, (2018)

http://dx.doi.org/10.1088/1361-6641/aac678

Cathodoluminescence studies of chevron features in semi-polar (11-22) InGaN/GaN multiple quantum well structures

Brasser C., Bruckbauer J., Gong Y.P., Jiu L., Bai J., Warzecha M., Edwards P. R., Wang T., Martin R. W.

Journal of Applied Physics Vol 123, (2018)

http://dx.doi.org/10.1063/1.5021883

Generated carrier dynamics in V-pit enhanced InGaN/GaN light emitting diode

Ajia Idris. A., Edwards Paul R., Pak Yusin, Belekov Ermek, Roldan Manuel A., Wei Nini, Liu Zhiqiang, Martin Robert W., Roqan Iman S.

ACS Photonics Vol 5, pp. 820-826, (2018)

http://dx.doi.org/10.1021/acsphotonics.7b00944

Multi-wavelength emission from a single InGaN/GaN nanorod analyzed by cathodoluminescence hyperspectral imaging

Kusch Gunnar, Conroy Michele, Li Haoning, Edwards Paul R., Zhao Chao, Ooi Boon S., Pugh Jon, Cryan Martin J., Parbrook Peter J., Martin Robert W.

Scientific Reports Vol 8, (2018)

http://dx.doi.org/10.1038/s41598-018-20142-5

Eu-Mg defects and donor-acceptor pairs in GaN : photodissociation and the excitation transfer problem

Singh A K , O'Donnell K P, Edwards P R, Lorenz K, Leach J H, Boćkowski M

Journal of Physics D: Applied Physics Vol 51, (2018)

http://dx.doi.org/10.1088/1361-6463/aaa1cc

Luminescence of Eu³⁺ in GaN(Mg, Eu): transitions from the ⁵D₁ level

Singh A. K., O'Donnell K. P., Edwards P. R., Cameron D., Lorenz K., Kappers M. J., Boćkowski M., Yamaga M., Prakash R.

Applied Physics Letters Vol 111, (2017)

http://dx.doi.org/10.1063/1.5001143

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Research interests

My research is focussed on the use of spectroscopic and microscopic methods in the analysis of semiconductors. The main materials of current interest to me are those based on the group III nitride quaternary system, Al_xGa_yIn_(1-x-y)N, and in particular nano-scale structures based on them. These have applications in many different areas, including solid-state lighting, data storage, communications and water purification. The techniques I use to study these materials include photoluminescence and electroluminescence spectroscopy, as well multiple modes of scanning electron microscopy (such as cathodoluminescence, electron beam-induced current and X-ray microanalysis). I am also interested in the application of multivariate statistical analysis techniques in the processing of the multidimensional data that these experimental methods yield.

Professional activities

Microscopy & Microanalysis 2018

Invited speaker

5/8/2018

PDI Topical Workshop on Cathodoluminescence of Semiconductor Nanostructures

Participant

16/4/2018

UK Nitrides Consortium Winter Conference 2018

Speaker

10/1/2018

12th International Conference on Nitride Semiconductors (ICNS-12)

Participant

23/7/2017

Microscience Microscopy Congress (MMC2015)

Invited speaker

2/7/2015

13th Australian Microbeam Analysis Symposium

Invited speaker

12/2/2015

more professional activities

Projects

Light-controlled manufacturing of semiconductor structures: a platform for next generation processing of photonic devices

Dawson, Martin (Co-investigator) Edwards, Paul (Co-investigator) Martin, Robert (Co-investigator) Watson, Ian (Co-investigator)

"This Platform Grant (PG) will apply our internationally-leading expertise in structured illumination and hybrid inorganic/organic semiconductor optoelectronic devices to create new opportunities in the rapidly developing field of light-controlled manufacturing. Structured illumination fields can in principle be obtained from both inorganic (GaN) and organic LEDs, implemented on a macroscale via relay optics, or demagnified to a microscale. Novel manufacturing with photopolymerisable materials can firstly involve use of structured illumination as a novel means to control motorised stages. This technique can be combined with pattern-programmable UV excitation for mask-free photolithographic patterning, continuous photo-curing over larger fields, localised photochemical deposition, or other forms of photo-labile assembly. Process variants can also be envisaged in which arbitrarily positioned fluorescent objects or markers are 'hunted', and then subject to beam excitation for photocuring or targeted photoexcitation. This method could be used, for example, to immobilise individual colloidal quantum dots for use as emitters in quantum technology applications. Multifunctional devices with sensing ability, such as organic lasers for explosives detection, represent another excellent example of automated devices operating under remote conditions. Further examples of the envisaged uses of this technology include: [1] LED microdisplay asset tags for management of high-value objects (artworks, nuclear fuel containers). [2] Passive asset tags containing unique micro-patterns of fluorescent objects (eg. colloidal quantum dots, organic macromolecules) for higher-volume, anti-counterfeiting applications. [3] Customisable continuous-flow micro-reactors for fine chemical manufacturing. [4] Energy harvesting micro-modules to power other autonomous microsystems, where we will focus on organic PV and ambient-radiation (RF) approaches."

Period 01-Jul-2017 - 30-Jun-2021

Quantitative non-destructive nanoscale characterisation of advanced materials

Hourahine, Benjamin (Principal Investigator) Edwards, Paul (Co-investigator) Roper, Richard (Co-investigator) Trager-Cowan, Carol (Co-investigator) Gunasekar, Naresh (Researcher)

"To satisfy the performance requirements for near term developments in electronic and optoelectronic devices will require pioneering materials growth, device fabrication and advances in characterisation techniques. The imminent arrival of devices a few atoms thick that are based on lighter materials such as graphene or boron nitride and also advanced silicon and diamond nano-structures. These devices pose new challenges to the currently available techniques for producing and understanding the resulting devices and how they fail. Optimising the performance of such devices will require a detailed understanding of extended structural defects and their influence on the properties of technologically relevant materials. These defects include threading dislocations and grain boundaries, and are often electrically active and so are strongly detrimental to the efficiency and lifetimes of nano-scale devices (a single badly-behaved defect can cause catastrophic device failure). These defects are especially problematic for devices such as silicon solar cells, advanced ultraviolet light emitting diodes, and advanced silicon carbide and gallium nitride based high power devices (used for efficient switching of large electrical currents or for high power microwave telecoms). For graphene and similar modern 2D materials, grain boundaries have significant impact on their properties as they easily span the whole size of devices. Resolving all of these problems requires new characterisation techniques for imaging of extended defects which are simultaneously rapid to use, are non-destructive and are structurally definitive on the nanoscale. Electron channelling contrast imaging (ECCI) is an effective structural characterisation tool which allows rapid non-destructive visualisation of extended crystal defects in the scanning electron microscope. However ECCI is usually applied as a qualitative method of investigating nano-scale materials, has limitations on the smallest size features that it can resolve, and suffers from difficulties in interpreting the resulting images. This limits this technique's ability to work out the nature of defects in these advanced materials. We will make use of new developments in energy resolving electron detectors, new advances in the modelling of electron beams with solids and the knowledge and experience of our research team and partners, to obtain a 6 fold improvement in the spatial resolution of the ECCI technique. This new energy-filtered way of making ECCI measurements will radically improve the quality of the information that can be obtained with this technique. We will couple our new capabilities to accurately measure and interpret images of defects to other advanced characterisation techniques. This will enable ECCI to be adopted as the technique of choice for non-destructive quantitative structural characterisation of defects in a wide range of important materials and provide a new technique to analyse the role of extended defects in electronic device failure."

Period 01-Jun-2017 - 30-Nov-2020

Doctoral Training Partnership (DTA - University of Strathclyde) | Bryce, Christopher

Martin, Robert (Principal Investigator) Edwards, Paul (Co-investigator) Bryce, Christopher (Research Co-investigator)

Period 01-Oct-2014 - 01-Aug-2018

Hysteretic photochromic switching (HPS) of europium-magnesium defects in gallium nitride: a potential route to a new solid-state qubit

O'Donnell, Kevin (Principal Investigator) Edwards, Paul (Co-investigator)

"Doping is the incorporation of chosen atomic impurities to make a material behave better or differently. When Shuji Nakamura developed a method of producing electrically conducting GaN by activating magnesium (Mg) atoms, he continued a tradition fundamental to all modern electronic devices. Mg doping of GaN allowed production of p-n junctions for today's ubiquitous 'white' light-emitting diodes (LED) and won Nakamura a share in the 2014 Physics Nobel prize. In the same way, europium (Eu) doping of oxide phosphors provided the necessary red optical emission in the 'fluorescent' lamps of a previous lighting revolution. We now propose to take the science of Eu-doped GaN beyond the limited goal of improving red III-nitride LEDs. We aim to explore the potential of hysteretic photochromic switching (HPS), recently discovered by us in GaN co-doped with Eu and Mg, to form the basis of a new solid state qubit or quantum bit.
First trials of rare earth (RE-) doped semiconductors, carried out in the late 1980's, suggested that materials with a wider band gap would show better high-temperature performance, thus favouring II-VI materials and III-nitrides over conventional semiconductors like silicon. However it was not until the present century that III-N semiconductors, grown as high-quality epitaxial thin films on sapphire, were good enough to test this conjecture; another decade passed before Fujiwara demonstrated an LED based on GaN doped with Eu during growth (2010).
Extensive comparative studies of Eu doping methods by the proposer and coworkers in the decade 2001-2011 established that, while such thick GaN:Eu samples could produce brighter overall emission, material produced by ion implantation, followed by annealing, was actually more efficient per dopant ion, by up to 400 times at low temperatures. We also showed that the defect responsible for the GaN:Eu red LED emission was the 'prime' defect, Eu2, consisting of an isolated Eu ion on a Ga lattice site. The commoner Eu1 defect has a more complex emission spectrum, suggesting a Eu atom perturbed by a lattice defect, such as a vacancy or interstitial atom. The total number of such complex centres reported in the GaN:Eu literature is larger than 10.
While attempting to improve the light emission advantage further by implanting Eu in p-type or n-type GaN templates, we discovered hysteretic photochromic switching (HPS) in GaN(Mg):Eu: p-type, Mg-doped GaN samples implanted with Eu ions and annealed. The HPS shows itself in the temperature dependence of the photoluminescence spectrum. At room temperature, the dominant emission, due to the centre Eu0, shows a sharp line at 619 nm. For comparison, Eu1 has a peak at 622 nm and Eu2 at 621 nm. On cooling the sample, the Eu0 intensity increases, as expected, until about 230 K, when it appears to saturate. Below 30 K, we observe a surprising rapid decline of Eu0 as the temperature decreases towards the base temperature of the cooling system. At the same time, an Eu1-like spectrum emerges and effectively replaces Eu0 at 11 K. We deduce that Eu0 somehow switches to Eu1 on cooling over a narrow temperature range. This switching does not reverse if the temperature is then increased from 11 K through 30 K. In fact, Eu1 fades rather slowly, allowing Eu0 to reappear only above ~ 100 K; this is hysteresis. Sample emission is maximum at about 200 K and then fades, reversibly, between 230 K and room temperature. The occurrence of photochromic switching near 20 K on cooldown followed by luminescence hysteresis on warming is given the acronym HPS (hysteretic photochromic switching).
The surprises continue: for samples cooled in the dark, switching from Eu0 to Eu1 can be seen in the time domain; and a resonance line appears at an intermediate wavelength between Eu0 and Eu1. The proposed project aims to determine if the resonance is an actual superposition of Eu0 and Eu1, promising a novel and simple solid state qubit based on Mg acceptor defects."

Period 01-Dec-2015 - 03-Jul-2019

Nanoanalysis for Advanced Materials and Healthcare - EPSRC strategic equipment

Martin, Robert (Principal Investigator) Edwards, Paul (Co-investigator) Faulds, Karen (Co-investigator) Florence, Alastair (Co-investigator) Graham, Duncan (Co-investigator) Sefcik, Jan (Co-investigator) Ter Horst, Joop (Co-investigator) Trager-Cowan, Carol (Co-investigator) Uttamchandani, Deepak (Co-investigator) Wark, Alastair (Co-investigator)

This proposal seeks funding to deliver enhanced capability for characterising and assessing advanced nanomaterials using three complementary, leading edge techniques: Field-emission microprobe (EPMA), combined Raman/multiphoton confocal microscope (Raman/MP) and small angle X-ray scattering (SAXS). This suite of equipment will be used to generate a step-change in nanoanalysis capability for a multi-disciplinary team of researchers who together form a key part of Strathclyde's new Technology and Innovation Centre (TIC). The equipment will support an extensive research portfolio with an emphasis on functional materials and healthcare applications. The requested equipment suite will enable Strathclyde and other UK academics to partner with other world-leading groups having complementary analytical facilities, thereby creating an international collaborative network of non-duplicated facilities for trans-national access. Moreover the equipment will generate new research opportunities in advanced materials science in partnership with the National Physical Laboratory, UK industry and academia.

Period 08-Nov-2015 - 07-Nov-2019

University Of Strathclyde - Equipment Account

Gachagan, Anthony (Principal Investigator) He, Wenlong (Principal Investigator) Jaroszynski, Dino (Principal Investigator) Martin, Robert (Principal Investigator) McArthur, Stephen (Principal Investigator) McArthur, Stephen (Principal Investigator) Connolly, Patricia (Co-investigator) Edwards, Paul (Co-investigator) Faulds, Karen (Co-investigator) Florence, Alastair (Co-investigator) Graham, Duncan (Co-investigator) Leithead, William (Co-investigator) Sefcik, Jan (Co-investigator) Ter Horst, Joop (Co-investigator) Trager-Cowan, Carol (Co-investigator) Uttamchandani, Deepak (Co-investigator) Wark, Alastair (Co-investigator)

"We propose to undertake an essential and cost effective upgrade of an existing high-power femtosecond laser system at Strathclyde to increase its output power, improve its stability and provide it with the necessary beam control and diagnostics systems to evaluate its performance and control (adjust) several important output beam parameters. The upgrade comprises a cryogenic cooler, to improve the power dissipation and thermal stability of the final laser amplifier Ti:sapphire crystal, a high-energy pump laser for the final amplifier, a wavefront sensor and deformable mirror system, to measure and control the wavefront phase, and an integrated 3rd-order cross-correlator, to measure the laser pulse contrast. The diagnostic systems are necessary to optimise the laser parameters and achieve the desired properties at focus. The cryo-cooler allows cooling of the final amplifier crystal to be increased from 28 W to 80 W, which enables the output power of the laser to be increased to 40 TW using the new high-energy pump laser. The upgraded will improve stability, increase intensity and shorten set-up and alignment times, thus increasing the usable time of the laser system to allow better use of the system and the beamline facilities at Strathclyde. The upgraded laser will be used to deliver the objectives of a Critical Mass proposal (submitted simultaneously) that is part of the ALPHA-X project, which involves 5 universities (Strathclyde, Glasgow, St Andrews, Dundee & Lancaster), and external Collaborators. The research programme includes a study of collective radiation-beam-plasma interactions at high field intensities, the production of ultra-short duration high brightness particle beams from the laser-plasma wakefield accelerator (LWFA), development of new methods of producing coherent and incoherent radiation, and applications of the sources. The applications programme involves an investigation of using high energy electrons for radiotherapy and also methods to produce medical radio-isotopes for medical imaging. The facility will also be used as a platform for engaging with industry through proof-of-concept projects. The upgraded facilities will be transferred to the SUPA Scottish Centre for the Application of Plasma-based Accelerators (SCAPA) when the facility has been constructed."

Period 01-Nov-2014 - 28-Feb-2023

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