Climate change attributed to the emission of carbon dioxide from burning coal, oil and gas has stimulated policies which encourage the use of renewable energy via tax concessions or feed-in tariffs. These are necessary because the cost of renewable energy is more than that of energy derived from fossil fuels. The potential of photovoltaics (PV) is enormous, with sunlight delivering the world's annual energy needs every 15 minutes. Unfortunately, in most circumstances, no PV technology yet delivers adequately low cost electricity. Silicon photovoltaics (PV) are a major renewable technology, accounting for ~90% of the PV market. The present industry view is that silicon will continue to dominate the market for the foreseeable future. Apart from the capital cost, the key parameters affecting cost per kWh are efficiency and working life. The efficiency of a cell is limited by the portion of the spectrum it can use. For a simple (single-junction) cell this fundamental limit is ~30%. Many ideas which aim to go beyond this have been researched but the essential combination of low cost, long life and efficiency have proved very elusive. Commercial modules made from low cost multi-crystalline silicon generally have efficiencies in the range 13 to 16%. Commercial production using high quality (more expensive) silicon reaches 20%, where the world record efficiency for a cell is 25.8%. From our experience of silicon materials research projects over the past five or so years, we believe it will be possible to enhance the carrier lifetime of cheaper forms of silicon to provide substantially higher production conversion efficiencies of ~22%. For domestic installation - where grid parity is regarded as matching the utility supplier's price - latest figures suggest this efficiency is sufficient for parity at latitudes of up to 60 degrees from the equator. This project unites three UK silicon PV groups with four materials manufacturers, a major cell manufacturer, two materials characterisation companies, and three leading international university groups to work on some of the most pertinent issues in silicon PV materials. We aim to provide underlying science which will enable silicon PV to produce electricity at lower prices than traditional generating plants. The quality of silicon, as characterised by the minority carrier lifetime, places the upper limit on the efficiency that can be achieved. Cell processing is sufficiently mature to be able to make high efficiency cells provided the starting material is of high quality. Simplistically, the aim of this project is to remove defects which act as recombination centres and limit the efficiency of silicon PV cells. We are developing novel new methods of impurity gettering and defect passivation which have the potential to remove recombination centres which remain after existing processes. The project will also further understanding of the fundamental properties of defects in silicon, including the role of nano-precipitates in recombination, factors which prevent the fundamental carrier lifetime of silicon being reached, and the thermodynamics of impurity-dislocation interactions.

Carbon dioxide produced by burning fossil fuels such as oil and gas is building up in the atmosphere and causing the planet to warm. The oceans have absorbed more than 90% of the heat trapped on the planet to date. However, this heating also causes the ocean to expand, leading to rising sea level and consequently to an increased risk to and vulnerability of people and industries located near the coast. Understanding how much sea level will change into the future allows us to plan accordingly the defences we need to install in order to safeguard the infrastructure and livelihoods of our coastal communities. Warming of the ocean is not geographically uniform however, as ocean currents move heat around the globe. This leads to contrasting changes in ocean temperature and sea level (affecting coastal communities and assets). By the end of the century, some regions may experience very large sea level rises of up to a metre while others will see far less (or even a lowering). This science program will use observations made from research ships and computer models of the ocean to understand where the ocean takes up heat from the atmosphere and how ocean currents transport and redistribute that heat. To study ocean currents we need a 'tracer' - something that is placed in and moves with the flow, like a chemical dye. Although not intentionally for this purpose, three varieties of tracers have been added to the atmosphere since the 1950s and have since gradually been absorbed into the ocean, and redistributed by ocean currents. These are radioactive carbon (produced by mid 20th century nuclear bomb tests), chlorofluorocarbons (historically used in refrigerators and aerosol cans, and which caused an expansion of the Ozone Hole) and more recently sulphur-hexafluoride (formerly found in tennis balls but now predominantly used in electrical industries as an insulator). These tracers have entered the ocean as distinct pulses at different times, forming a fortuitous experiment we can now observe. We will use high-precision equipment to measure these tracers in the Atlantic and Southern Oceans and collaborate with international partners to track their global fate. We will use these observations to estimate the rate at which heat is being absorbed and re-distributed throughout the ocean and to assess and improve climate model predictions of regional sea level rise.

When an impurity atom in a semiconductor crystal has more (or fewer) valence electrons than the atom it replaces, it can donate one or more electrons to (or accept them from) the crystal lattice. The deliberate addition of such impurities, called dopants, is the traditional means of generating mobile charge carriers (negatively-charged electrons or positively-charged holes) within semiconductor devices, including the silicon-based metal-oxide-semiconductor field-effect transistors (MOSFETs) and compound semiconductor high-electron-mobility transistors (HEMTs) ubiquitous in modern electronics. High-mobility, gallium-arsenide-based HEMTs in particular, which can be made from ultrahigh-purity wafers grown by molecular beam epitaxy (MBE), have also been instrumental in the discoveries of new physics, including the fractional quantum Hall (FQH) effect, microwave-induced resistance oscillations, Wigner solid phases in magnetic field, ballistic transport and conductance quantisation in one-dimensional channels, single-electron quantum dots, Kondo physics, spin-based solid-state qubits, possible excitonic superfluidity in double-quantum-well structures, and possible non-Abelian statistics in certain novel FQH states. Even with the technique of modulation doping, where dopants are placed far away from the conducting channel, disorder due to the ionised dopants can still be felt by the carriers in a high-purity wafer, and this disorder can interfere with phenomena being studied. However, these intentional dopants are not necessary if one uses instead an external electric field to electrostatically induce a two-dimensional electron gas (2DEG) or hole gas (2DHG) at the semiconductor heterointerface. This electric field can be applied with electrostatic gates on the front and/or back side of devices. Although the proof-of-principle demonstration of undoped devices (which required only one working device) was reported more than eighteen years ago by Bell Labs (USA), the complex cleanroom fabrication process and the ensuing very low yield of working devices have prevented the use of undoped devices from becoming mainstream. Over the last three years, our group has made a number of technological breakthroughs which allow a 90+% yield of working devices, including Hall bars and nanostructures (e.g., quantum dots). This yield is now high enough to have research projects depend on a steady, reliable supply of high-quality samples. To capitalise on this success, we propose to combine our ability to fabricate such devices on demand with our expertise in MBE semiconductor wafer growth and millikelvin temperature measurements to further progress on two of the topics listed above, the fractional quantum hall effect and spin-based solid-state qubits. Many "exotic" FQH states present in the second Landau level do not fit the Laughlin/Jain theory which describes "conventional" FQH states, and are particularly sensitive to dopant-induced disorder. Our experimental programme will shed light on the nature of these states, particularly the famous state at filling factor 5/2 and its possible non-Abelian properties. Gate-defined electron spin qubits in GaAs were once amongst the forerunner systems for the realisation of a quantum computer. However, this system suffers from the presence of hyperfine interactions and charge noise, both of which cause spin decoherence on timescales too short for a practical quantum computer. Our experimental programme will demonstrate how both hyperfine interactions and charge noise are significantly reduced when gate-defined double quantum dots are fabricated from undoped 2DHGs. Our proposed work will yield fundamental insights into physical phenomena not easily accessible using even the highest quality doped heterostructures.

Around 11 million people developed tuberculosis (TB) in 2021, and 1.6 million died from the disease. Current control strategies are insufficient, with global TB incidence falling by only 2% per year. One reason for the slow decline may be widespread reliance on passive case detection - requiring people with TB to present to healthcare services with symptoms. This means that people can be infectious for months or years before diagnosis, and an estimated 40% of incident TB was not diagnosed in 2021. Active case finding (ACF) - the systematic screening of high-risk groups or populations - is one way to find people with TB earlier, leading to reductions in transmission. The World Health Organization recommends ACF in areas with a high prevalence of TB. Recent National Strategic Plans from countries as diverse as South Africa, Uganda, and India contain plans to scale-up ACF in high risk populations. Despite the scaling up of ACF activities, considerable uncertainty remains as to their likely impact, and how it varies between approaches and settings. Three randomised control trials (RCTs) estimating the impact of ACF on transmission have been conducted. One trial achieved an impressive 50% (95% CI 22-68%) reduction in the prevalence of infection in children (a proxy for transmission), demonstrating that community ACF can be a highly effective in reducing transmission. The other trials used less intensive intervention approaches, and found no evidence for reductions in transmission. A fourth RCT found a reduction in TB prevalence, but did not estimate reductions in transmission. Mathematical modelling suggests that the differences between the trial results cannot be explained by differences in the tests used or numbers of cases detected. There is a need to understand factors that affect the reductions in TB incidence achieved through ACF, and to identify less intensive and expensive ACF approaches that can lead to reductions in transmission. Mathematical modelling can be used to predict the impact of ACF on TB incidence. However, assumptions typically made in models may not be correct, and models of ACF have rarely been validated using empirical data. In particular, we have identified three factors that may alter the impact of ACF on TB incidence: A) People who have been screened in previous rounds may be more or less likely to seek or accept screening. B) Coverage tends to be lower in men than in women, despite higher TB prevalences in men. C) The probability of participating in ACF may be higher for people who were closer to seeking care and receiving a diagnosis passively. The impact of these factors may vary by intervention design and setting.

Sea level change is one of the most widely known and potentially serious consequences of climate change due to emissions of greenhouse gases. It concerns both the public and policymakers, because of its adverse impact on the populations and ecosystems of coastal and low-lying areas. This impact is expected to increase for centuries to come. Sea water expands as it warms in a process known as thermal expansion. Thermal expansion due to changes in the amount of heat entering the ocean is the largest contributor to sea level rise projected for the 21st century. Regional sea level is also affected by changes in precipitation, evaporation and winds over the ocean because, along with heating, these affect ocean density and currents. The contraction of glaciers and ice sheets expected in a warming climate is another important contributor to projected global and regional sea level change, but it is a different scientific subject which we do not propose to address directly here. Computer climate models disagree in their projections of sea level change. This means that we are not able to make precise predictions of sea level rise on average over the globe. Moreover, while all models predict that some regions will experience a larger rise than average and others a smaller rise than average, they do not agree on these geographical patterns. A large part of the uncertainty is related to the different behaviour of the various models in response to the changing effects of heat, water and winds. They behave differently because different assumptions have been made in their formulations, reflecting a lack of precise knowledge. This project aims to study these uncertainties, by detailed analysis, using new techniques, of how the ocean models respond to particular inputs, and by comparison with theory and observations. Our aim is thus to reduce the range of the projections. Any such reduction is potentially of large societal and economic benefit; for example, planning decisions need to be made concerning coastal infrastructure that may last for decades and cost billions of pounds.