The goal of this proposal is to develop advanced fabrication processes for Gallium Nitride (GaN) and related materials (AlN and InN), collectively the III-Nitrides, for the 21st Century manufacturing industries. The III-Nitrides are functional materials that underpin the emerging global solid state lighting and power electronics industries. But their properties enable far wider applications: solar energy conversion by photovoltaic effect and water splitting, water purification, sensing by photonic and piezoelectric effects and in non-linear optics. Many applications of these functions of the III-Nitrides are enhanced, even enabled by creating three dimensional (3D) nanostructures. As such, the particular focus of the proposed research is to develop and nanostructuring processes on a manufacturing scale and to unlock the potential of these properties of the III-Nitride semiconductors in a range of innovative materials and devices. The research will address and resolve 1) the need of industry to be able to scale-up laboratory-based results based on individual piece or wafer fragments to batches of wafers of up to 6 inches in diameter, 2) the need to be able to design devices that are robust with the manufacturing tolerances, and 3) the need to rapidly characterise the devices to increase packaging yield. Potential commercial exploitation of the manufacturing processes and innovative materials and devices will be aided and led by the applicants' company partners. The programme of research opens with developing the core capability of wafer-scale (up to 6 inch) nanopatterning by nanoimprint lithography and the newly developed technique of Displacement Talbot Lithography, a potentially disruptive technology for generating nanostructures. These lithographic techniques will then be integrated with additive and subtractive processes to form 3D nanostructures across whole wafers. In a major application, the developed nanofabrication techniques will be used in developing manufacturing processes for the growth by metal organic vapour phase epitaxy (MOVPE) of non-polar and semi-polar GaN templates to address the persistent problem of the quantum confined Stark effect limiting the efficiency of light emitting diodes (LEDs) and GaN based laser diodes. The computer aided design method known as Designing Centering will be developed for process optimisation to maximise the yield of nanostructured devices (initially LEDs). Another activity will be to explore the use of electron beam and optical techniques, which are capable of characterising materials and devices on the deeply sub-micron scale, as production tools for screening materials and part-processed devices. The combination of wafer-scale nanofabrication techniques, advanced MOVPE growth, characterisation methods and Design Centering will then be deployed in the design and manufacture of innovative and emerging devices including core-shell structures for LEDs and photovoltaic applications, and nano-beam sensors that incorporate photonic crystals. Having established the core capability for the III-Nitrides, it will be extended to nanostructuring other semiconductors, notably InP and related materials as used in the manufacture of devices for optical fibre telecommunications.

This proposal seeks funding to create a Centre for Doctoral Training (CDT) in Connected Electronic and Photonic Systems (CEPS). Photonics has moved from a niche industry to being embedded in the majority of deployed systems, ranging from sensing, biophotonics and advanced manufacturing, through communications from the chip-to-chip to transcontinental scale, to display technologies, bringing higher resolution, lower power operation and enabling new ways of human-machine interaction. These advances have set the scene for a major change in commercialisation activity where electronics photonics and wireless converge in a wide range of information, sensing, communications, manufacturing and personal healthcare systems. Currently manufactured systems are realised by combining separately developed photonics, electronic and wireless components. This approach is labour intensive and requires many electrical interconnects as well as optical alignment on the micron scale. Devices are optimised separately and then brought together to meet systems specifications. Such an approach, although it has delivered remarkable results, not least the communications systems upon which the internet depends, limits the benefits that could come from systems-led design and the development of technologies for seamless integration of electronic photonics and wireless systems. To realise such connected systems requires researchers who have not only deep understanding of their specialist area, but also an excellent understanding across the fields of electronic photonics and wireless hardware and software. This proposal seeks to meet this important need, building upon the uniqueness and extent of the UCL and Cambridge research, where research activities are already focussing on higher levels of electronic, photonic and wireless integration; the convergence of wireless and optical communication systems; combined quantum and classical communication systems; the application of THz and optical low-latency connections in data centres; techniques for the low-cost roll-out of optical fibre to replace the copper network; the substitution of many conventional lighting products with photonic light sources and extensive application of photonics in medical diagnostics and personalised medicine. Many of these activities will increasingly rely on more advanced systems integration, and so the proposed CDT includes experts in electronic circuits, wireless systems and software. By drawing these complementary activities together, and building upon initial work towards this goal carried out within our previously funded CDT in Integrated Photonic and Electronic Systems, it is proposed to develop an advanced training programme to equip the next generation of very high calibre doctoral students with the required technical expertise, responsible innovation (RI), commercial and business skills to enable the £90 billion annual turnover UK electronics and photonics industry to create the closely integrated systems of the future. The CEPS CDT will provide a wide range of methods for learning for research students, well beyond that conventionally available, so that they can gain the required skills. In addition to conventional lectures and seminars, for example, there will be bespoke experimental coursework activities, reading clubs, roadmapping activities, responsible innovation (RI) studies, secondments to companies and other research laboratories and business planning courses. Connecting electronic and photonic systems is likely to expand the range of applications into which these technologies are deployed in other key sectors of the economy, such as industrial manufacturing, consumer electronics, data processing, defence, energy, engineering, security and medicine. As a result, a key feature of the CDT will be a developed awareness in its student cohorts of the breadth of opportunity available and the confidence that they can make strong impact thereon.

Micro-displays with compact screens of <= 1/4 inch diagonal length have wide ranging applications in smart watches, smart phones, augmented reality & virtual reality (AR & VR) devices, Helmet Mounted Displays (HMD), and Head-Up Displays (HUD). Their individual pixel elements typically consist of a large number of microscale visible emitters (which are currently microLEDs). The global micro-display market has been predicted to reach $4.2 billion by 2025 at a Compound Annual Growth Rate (CAGR) of 100%. However, the significantly increasing demands on microdisplays are pushing the requirements for ultra-high resolution and ultra-high efficiency. Current microdisplays are far from satisfactory, as a number of fundamental challenges cannot be met by any existing technologies. Therefore, a disruptive technology needs to be developed. Visible light communication (VLC) is an emerging technology, in principle offering approximately 300 THz of license free bandwidth that is four orders of magnitude larger than that available in current RF based Wi-Fi or 5G. Considering the highly congested nature of current RF based Wi-Fi, it is expected that VLC would be the leading candidate to offer a complementary solution. Unfortunately, the current approach to the fabrication of VLC is substantially limited to visible LED technologies with conventional electrical driving methods. This approach suffers from a number of insurmountable barriers. Therefore, the performance of current VLC is far below requirements. Global Market Insights has forecasted that the VLC market will exceed $8 billion by 2030. We propose a Centre-to-Centre consortium consisting of ten leading academics from three universities in the UK (Sheffield; Strathclyde; Bath) and two universities in USA (Harvard; Massachusetts Institute of Technology) to develop a novel integration technology in order to achieve the ultimate micro-display systems and the ultimate visible light communication systems. Unlike any existing photonics & electronics fabrication approaches, we propose a completely different approach to monolithically integrate microscale laser diodes (uLDs) and high electron mobility transistors (HEMTs) on a single chip, where each uLD is electrically driven by individual HEMTs. This will allow us to achieve devices/systems which are impossible to obtain by any existing approaches.

Global demand for high power microwave electronic devices that can deliver power densities well exceeding current technology is increasing. In particular Gallium Nitride (GaN) based high electron mobility transistors (HEMTs) are a key enabling technology for high-efficiency military and civilian microwave systems, and increasingly for power conditioning applications in the low carbon economy. This material and device system well exceeds the performance permitted by the existing Si LDMOS, GaAs PHEMT or HBT technologies. GaN-based HEMTs have reached RF power levels up to 40 W/mm, and at frequencies exceeding 300 GHz, i.e., a spectacular performance enabling disruptive changes for many system applications. However, transistor reliability is driven by electric field and channel temperature, so self-heating means in practice that reliable devices can only be operated up to RF power densities of 10 W/mm in contrast to the 40 W/mm hero data published in the literature. Considerable concern also exists in the UK and across Europe that access to state-of-the-art GaN microwave technology is limited by US ITAR (International Traffic in Arms Regulation) restrictions. The most advanced capabilities for all elements of GaN HEMT technology, using traditional SiC substrates, epitaxy and device processing currently reside in the US, with restricted access by UK industry. The vision of Integrated GaN-Diamond Microwave Electronics: From Materials, Transistors to MMICs (GaN-DaME) is to develop transformative GaN-on-Diamond HEMTs and MMICs, the technology step beyond GaN-on-SiC, which will revolutionize the thermal management which presently limits GaN electronics. Challenges occur in terms of how to integrate such dissimilar materials into a reliable device technology. The outcome will be devices with a >5x increase in RF power compared to GaN-on-SiC, or alternatively and equally valuably, a dramatic 'step-change' shrinkage in MMIC or PA size, and hence an increase in efficiency through the removal of lossy combining networks as well as a reduction in power amplifier (PA) cost. This represents a disruptive change in capability that will allow the realisation of new system architectures e.g. for RF seekers and medical applications, and enable the bandwidths needed to deliver 5G and beyond. Reduced requirements for cooling / increased reliability will result in major cost savings at the system level. To enable our vision to become reality, we will develop new diamond growth approaches that maximize diamond thermal conductivity close to the active GaN device area. In present GaN-on-Diamond devices a thin dielectric layer is required on the GaN surface to enable seeding and successful deposition of diamond onto the GaN. Unfortunately, most of the thermal barrier in these devices then exists at this GaN-dielectric-diamond interface, which has much poorer thermal conductivity than desired. Any reduction in this thermal resistance, either by removing the need for a dielectric seeding layer for diamond growth, or by optimizing the grain structure of the diamond near the seeding, would be of huge benefit. Novel diamond growth will be combined with innovative micro-fluidics using phase-change materials, a dramatically more powerful approach than conventional micro-fluidics, to further aid heat extraction. An undiscussed consequence of using diamond, its low dielectric constant, which poses challenges and opportunities for microwave design will be exploited. At the most basic level, the reliability of this technology is not known. For instance, at the materials level the diamond and GaN have very different coefficients of thermal expansion (CTE). Mechanically rigid interfaces will need to be developed including interdigitated GaN-diamond interfaces.

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.