Electronic and opto-electronic devices based on gallium nitride (GaN) form a multi-billion dollar industry across the world, including lighting (LEDs), power sources and communications (radar and 5G). One of the most challenging aspects of developing these devices commercially is the high density of defects - i.e. mistakes in the crystal's structure - found in most commercially grown GaN, such as dislocations and stacking faults. It is possible to grow GaN with fewer of these mistakes, but it is slow and expensive, and most devices therefore contain a high density of defects, which will affect device performance. In particular, all devices will contain either alloying elements (aluminium gallium nitride, AlGaN, and indium gallium nitride, InGaN, are made by alloying Al and In with Ga during growth) and/or doping elements (magnesium, Mg, is added to change the conduction properties of GaN, for instance for making LEDs) and these elements will interact with the defects, which can prevent the extra elements from having the intended impact or change the local properties of the material being grown in undesirable ways. We will study how alloying and doping elements interact with defects, in particular where larger or smaller numbers of these atoms are found relative to what is expected. We will seek to understand why these changes happen, and ultimately how they can be controlled, either to reduce the numbers of defects, or to reduce the harmful effects of the defects on the desired materials properties. Our project will link state-of-the-art experimental techniques with cutting edge theory and modelling approaches. The experimental data will allow us to examine the positions of individual atoms with exquisite detail, while the modelling will address problems which involve large numbers of atoms, something which standard approaches cannot manage. This combination of techniques will enable us to understand and control the materials in ways that are not possible with each technique independently, and which will feed into industrial processes.

Technological advances have led to the availability of electronic devices like laptops, mobile devices and global positioning systems. In order to increase performance, modern technology has followed the path of miniaturising the components to reduce the overall size of commercial devices. Following this trend, we have now reached the point where matter can be controlled at the smallest scale: the single atom. It is in this new realm of physics that unconventional effects take place: when we deal with structures composed of just a few atoms or when we manipulate single electronic charges, the physics follows rules described by quantum mechanics. A completely new range of effects take place and devices with novel functionalities can be created: the quantum information revolution seems to be within reach. A very exciting research field focuses on the study of nanostructures, entities whose dimensions are of the order of 0.000000001m. Such small structures can be used for controlling single particles of light: single photons. Conventional light sources emit a large number of photons in a wide angular range and are mainly used for lighting and imaging. The ability to control light at the single-photon level is technologically challenging but tremendously interesting. If we can store information encoded on single photons, we can transfer it at the speed of light with a guaranteed secure communication. Single-photon emitters also find applications in imaging and medical sensing. Unfortunately, many single-photon sources operate at very low temperatures, which require the use of liquid helium, which is expensive and inconvenient for real-world applications. A material called Gallium Nitride (GaN) offers opportunities to overcome these limitations. GaN is a semiconductor crystal, and defects in that crystal can act as single-photon emitters, as can indium gallium nitride (InGaN) nanostructures embedded in a GaN matrix. Such nanostructures can emit single photons at room temperature, across a very wide range of wavelengths. However, incorporating these emitters into practical devices is very challenging. They tend to form at random locations in the crystal, which makes it hard to ensure that a device contains an optimally-positioned single emitter and that the light is emitted in the desired direction with high efficiency, as required for applications. In this project, we will develop technologies which allow us to control where an emitter forms, and integrate those site-controlled emitters with structures which extract the light from the device efficiently and channel it in a desired direction. We will create devices where the light extraction structures are integrated with the electrical injection of charge carriers into the emitter. That means that we will be able to use an applied voltage to either drive the single-photon emission or to alter the wavelength (or colour) of the emitted photon. The approach we will take to improving light extraction uses technologies that are easily incorporated into a standard manufacturing routine. We will put mirror-like structures underneath the single-photon emitters; above them, on the crystal surface, we will place tiny rings of metal, which can act like a lens, directing the light into the application system. In addition to being relatively easy to manufacture, relative to other possible technologies, this approach has additional advantages: it avoids etching the GaN crystal, which can damage device performance, and it also places less stringent requirements on achieving a very specific wavelength from the single-photon emitter. The metallic ring also doubles up as a contact for electrical injection. Overall, this provides a scalable, robust route to creating a new quantum technology - which addresses UK government priorities for advanced materials and manufacturing, and represents a crucial step forward in the implementation of quantum emitters in real-life devices.

The research area of porous materials is extremely diverse, including inorganic materials, organic polymers, synthetic frameworks, biological tissues and composite systems. The variety of applications is equally wide ranging, including renewable energy, separation processes, carbon capture, catalysis, water purification, electronic materials and medicine. This requires combined expertise across multiple science and engineering disciplines, and access to specialist characterisation facilities to study both pore sizes and phenomena that can span multiple scales. A single institution cannot cover the full range of expertise, facilities and applications and a combined effort is therefore required. The EPSRC Network in Engineering Porous Materials at Multiple Scales (EPoMM) therefore aims to foster multiscale and applications- led collaboration between scientists and engineers that spans the entire engineering and physical sciences portfolio. These collaborations will inspire new research directions and new applications to achieve globally significant outcomes with academic, commercial and societal benefits. The vision of the ESPRC Network for Engineering Porous Materials at Multiple Scales (EPoMM) is to make the UK an internationally recognised beacon for multiscale porous materials research, where new collaborations are formed, new research directions are identified, expert advice can be sought, and innovations are commercialised.

Augmented reality (AR) has the power to seamlessly integrate the digital world with physical reality. It could provide surgeons with vital medical data as they operate, allow athletes to access training information seamlessly whilst playing sports and offers countless other opportunities in business, leisure and beyond. However, currently AR technologies are let down by the performance of microdisplays. AR devices must operate successfully not only in darkened rooms but also in bright sunlight, and must also be very small and run all day on one charge of a compact battery. Hence, enormous demands are placed on tiny light emitters in microdisplays in terms of brightness and efficiency. For AR to become a mass market technology, any new approach to microdisplays will need to not only meet these demands, but also allow easy manufacturing. Current light emitting diodes (LEDs) fail to meet these needs, since key materials which work well for larger area light emitters exhibit a drop in efficiency when the device size is shrunk to meet the demands of form factor and resolution imposed by AR. However, in terms of large scale LEDs, devices based on gallium nitride (GaN) have been tremendously successful, transforming the lighting industry. GaN LEDs also show much lower drops in efficiency with reduction in size than other similar materials. Unfortunately, these GaN LEDs are highly efficient only for light emission in the blue region of the spectrum. Green, amber and particularly red devices based on the same materials have much lower efficiencies, but are needed to create full colour microdisplays. In white LED light bulbs, blue light is converted to other colours by phosphor materials, but these phosphors are manufactured as bulky micron sized powders, too coarse to be used in microLEDs. In this project, we will take a new approach to integrating alternative, nanometre-scale phosphor particles (ca. 100 atoms wide) with nitride LEDs. Our alternative phosphors are highly luminescent colloidal nanoparticles, synthesised straightforwardly in solution using scalable techniques and easily made into nanoparticle inks. These materials are already used in "QLED" display technologies, but display manufacture is complex and the difficulties increase substantially as the device shrinks. Our new concept is to use printing technologies to inject nanoparticles not onto the surface of LEDs, but into nanoscale pores in the GaN itself. The nanoporous GaN materials are a very recent development and unique, scalable methods for their fabrication have been invented in our laboratory. By printing onto these porous scaffolds we will exploit capillary action to suck the nanoparticles into the desired region of the device, preventing spreading of the nanoparticle ink and hence achieving controlled manufacture straightforwardly at the required scale. In so doing, we will create a new optical composite material - a combination of the GaN and the highly luminescent nanoparticles - and by using the structure of the nanopores to align and control the array of nanoparticles, we will enable new and more sophisticated devices, for future display technologies such as AR in three dimensions.

"Semiconductors" are synonymous with "Silicon Chips". After all Silicon supported computing technologies in the 20th century. But Silicon is reaching fundamental limits and already many of the technologies we now take for granted are only possible because of Compound Semiconductors (CS). These include The Internet, Smart Phones, GPS and Energy efficient LED lighting! CSs are also at the heart of most of the new technologies expected in the next few years including 6G wireless, ultra-high speed optical fibre connectivity, LIDAR for autonomous vehicles, high voltage switching for electric vehicles, the IoT and high capacity data storage. CSs also offer huge opportunities for energy efficiency and net zero. CSs are often made in small quantities and using bespoke techniques and manufacturers have had to put together functions by assembling discrete devices. But this is expensive and for many of the new applications scale-up and integration, along the lines of the Silicon Chip, are needed CDT research will involve the science of large scale CS manufacturing, manufacturing integrated CS on Silicon and applying the manufacturing approaches of Silicon to CS; it will generate novel integrated functionality and all with an emphasis on finding environmentally sustainable manufacturing methods. CIVIC PRIORITY: This CDT is a fundamental part of the strategic development of the CS Cluster centred in South Wales, and in linking it to activity across the UK. It is part of a wider training strategy including apprenticeships, MScs and CPD, to train and upskill the entire workforce. The latest skills requirements have been identified by partner companies and through working with Welsh Government, CSconnected and the CS Applications Catapult The partners support the CDT financially and with their time. This is because the limiting factor to rapid cluster growth is skilled people. The expected PhD level jobs increase for the existing cluster companies alone would mop up all the students trained by this CDT. We provide a £2k stipend top-up to maximise recruitment from all backgrounds. However, the CDT does more - clusters are about cross-fertilisation of people and ideas and the CDT combines academics from 4 universities with leading and complementary expertise in CS. We form teams of two academics from different universities, one industry supervisor and the PhD student to create and carry out each PhD. The CDT also ensures the whole cohort regularly works together to exchange new knowledge and ideas and maintain breadth for each student. The UK and Welsh administrations see CS as an opportunity to boost the economy with high technology jobs and the UK government uses the CDT as part of its pitch to overseas companies to locate here. APPROACH and OUTCOMES: a 1+3 program where Year 1 (Y1) is based in Cardiff, with provision via taught lectures and transferable skills training, hands on and in-depth practical training and workshops led by University and Industry Partner staff. Following requests from Y2-4 students the industry workshops are presented in hybrid format so all Y2-4 students can further benefit from this program and where we now cycle presenters, companies and specific topics over 3 years. A dedicated training clean room allows rapid practical progress in a supportive environment, learning from doing, experts and the rest of the cohort and then an industry facing cleanroom, co-located with industry staff and manufacturing scale equipment, where students learn the future CS manufacturing skills. This maximises exchange of ideas, techniques and approach and the potential for exploitation. Both students and industry partners have praised the practical skills this produces. Y2-Y4 consist of an in depth PhD project, co-created with industry and hosted at one of the 4 universities, and specialised whole cohort training and events, including energy audit, research ethics and innovative outreach