Lighting the Future

Next time you change a tungsten filament light-bulb, give a brief thought to the amount of energy that bulb will have used up over its lifetime: more than 200 million Joules (about the same amount of energy as is contained in 3 tonnes of coal)! If you consider how many light bulbs must be in use in the world at this moment, it becomes clear that a huge amount of energy is spent keeping our homes and offices lit. In fact, about a fifth of electricity usage in the UK is for lighting. Hence, improvements in something as simple as light bulb efficiency could have an enormous impact on the UK's greenhouse gas emissions and use of fossil fuels.A new semiconductor material - gallium nitride (GaN) - provides a potential solution to the lighting problem. GaN is used to make white light-emitting diodes (LEDs). These solid state-light sources are already much more efficient than conventional tungsten filament light bulbs, and could potentially yield efficiency improvements of more than ten times (and be three times more efficient than compact fluorescent lamps). To achieve these vast improvements in efficiency, we need to thoroughly understand the material from which we make the LEDs, and how its structure, composition and properties influence LED performance. We also need to design devices which make the best possible use of everything we learn about the material. A large number of different factors influence the efficiency of LEDs, and in this programme, scientists from Cambridge, Manchester, Bath and Strathclyde are pooling their expertise to understand what limits the efficiency and find solutions which will benefit all of us, by providing sensibly-priced, highly-efficient lighting units which will be long-lasting and provide attractive high-quality light in homes and offices.To do this, we are breaking down the question of LED efficiency into a number of inter-linked scientific projects. GaN LEDs are based on thin layers of material grown on other materials such as silicon or sapphire. Electric current is passed into the active region of the LED, from which the light is emitted. The active region consists of very thin alternating layers of GaN and another semiconductor - indium gallium nitride (InGaN). The InGaN layers are only ten atomic layers thick and are called quantum wells. In the InGaN layers, positive and negative charge carriers become trapped and hence combine with one another giving out light. The GaN and InGaN crystals are not perfect, however, and defects in their structure can disrupt the light emission process, resulting in the production of heat rather than light and a reduction in LED efficiency. In the early years of our programme, we plan to tackle fundamental questions relating to light emission efficiency, by pursuing projects concentrating on the defects in the material, the detailed small-scale structure of the InGaN quantum wells and the electric fields which arise in those quantum wells. The effect of all of these factors will be dependent on the amount of electricity injected into the LED, and a major problem is that LED efficiency drops at high injection currents. Since high brightness LEDs for lighting require high electric currents, we will also need to understand this question before solid state lighting can reach its full potential.The new materials and structures we develop will have to be integrated into working LED devices, and the architecture of those devices is also a key factor affecting efficiency. Hence, another of our research projects will address device design. By bringing the new ideas we develop about materials and devices together we aim to produce LEDs that are highly efficient and thus beneficial to our environment, cheap to buy and, unlike compact fluorescent lamps, produce an attractive colour of light to make homes and offices pleasant and healthy places to be. In the end, we hope the products of our research really will be lighting your future!

Fully understanding and overcoming the factors limiting the internal quantum efficiency (IQE) of III-nitride LEDs, the primary objective of the project, is expected to result in IQEs of more than 90%. The impact of such LEDs on the lighting industry at every level cannot be overstated. White light sources with efficacies of 250 lumens/W or more, a factor of 2.5 greater than fluorescent tubes, could be produced consistently and cost-effectively. The effects of this technology on all sectors will be immense: * Industry and commerce throughout the UK will benefit from reduced electricity bills as a result of the uptake of energy-efficient lighting, increasing profits and boosting the UK economy. * The development of improved energy-efficient lighting can cut the energy used for lighting by up to 80% and give a reduction of up to 15% in the UK's total electricity usage, helping the UK Government reach its legally binding target of a 34% reduction in CO2 emissions by 2020 and reducing our dependence on foreign energy supplies. * The wider public will benefit from improved quality of life through provision of better quality, mercury-free, energy-saving lighting for homes and offices (bringing lower energy bills and environmental and health benefits). A successful research programme that contributes significantly to the introduction of LED lighting will inevitably place UK industry in a powerful position to exploit this exciting new technology. * The UK has over 1700 companies working in the lighting industry. * Whilst there is currently no major LED manufacturer in the UK, the barriers to new entrants in the field are low. The photovoltaic industry in Germany provides a comparable example. The project partners are involved in discussions with UK industry on establishing LED manufacturing capability. * The project partners have close links with III-nitride-based UK industry (e.g. Sharp Europe, IQE, QinetiQ, AIXTRON UK, RFMD UK, Enfis, PhotonStar LED and Forge Europa). These links will ensure that our research tackles major questions that are relevant to commercial needs and will provide multiple routes for commercial exploitation. (See letters of support). Our research has already had a major impact on some of these industries. For example, it has helped Aixtron Ltd. to sell many growth reactors and helped Forge Europa to grow by over 100% in the last three years. * The exploitation of the outputs of this programme will be ensured by the significant commercial and patent expertise of our personnel, combined with a strong industrial presence on our Steering Panel, our broad-ranging industrial links, and the availability of expert advice on IP and commercialisation from University Technology Transfer Offices. * We will offer cross-disciplinary training and industrial secondment opportunities to students and PDRAs, providing them with a broad base of scientific and transferable skills to take into future employment in UK industry. Alumni of the partner research groups are currently having significant impact as employees of UK industries. Public outreach activities are vital to ensure the acceptance and uptake of energy-efficient lighting. The project partners are both trained and experienced in science communications, and are currently involved in a broad range of outreach activities which they plan to extend during the project: * The Cambridge/Manchester research on LEDs has recently been highlighted in the EPSRC IMPACT! campaign and has had widespread press and TV coverage. * We will continue to raise awareness of energy-efficient lighting through public outreach activities (including, a proposed exhibit at the Royal Society Summer Exhibition), press releases and a dedicated interactive section of the project website. * The hosting of the main international nitride conference (ICNS) in 2011 in Glasgow provides an excellent platform to deliver key results to world-wide academia, industry and the local public.