Multifunctional III-nitride materials

New device materials: why?Lighting, public transport, manufacturing and personal computing - these are central to our modern lives. Unfortunately, right now, light bulbs waste 95% of the electricity we put into them, whereas the AC motors and power supplies used in transport and industry can waste up to 45% and the RAM in personal computers can waste tens of watts even when it isn't used. Given our rising demand for energy but limited fossil fuel supplies, this is a major problem! However, major energy savings can be made by improving just two basic types of electrical device; light-emitting diodes (LEDs) and transistors. In particular, we need much more efficient green LEDs (to be combined with existing red and blue LEDs to produce white light) and we need transistors that can run efficiently at very high powers and frequencies without wasting energy on standby. Such devices could also be shrunk and adapted for use in ultra-high-density computer memory. However, current materials cannot reach the performance needed for these devices, so better materials must be found. What do novel nitrides have to offer? Materials in electronic devices usually have just one main function. For example, gallium nitride works as a semiconductor in blue LEDs and high-power transistors. However, this proposal centres on creating multifunctional nitride-based materials for use in new, improved devices. Currently, some exotic materials can simultaneously act as semiconductors, ferroelectrics (i.e. they have a spontaneous, reversible electric polarization) and as magnets, but most of them are unstable, difficult to manufacture or don't work at room temperature. Instead, existing nitride semiconductors could be modified by adding metals like scandium, which generate tiny distortions in the crystal structure. These materials are particularly exciting because the distortions can produce new ferroelectric and magnetic properties which nobody thought could coexist in the nitrides. At low metal concentrations, the new materials are stable and can emit light of the right colour to replace existing, highly defective active regions in green LEDs. At higher metal concentrations, the distortions line up and the entire crystal structure changes. Such materials could then be used in transistors, where they should produce a thin switchable layer of electrons, giving a very low 'on' resistance without drawing power when 'off'. Alternatively, by detecting the presence or absence of this electron layer, we could take away the transistor 'source' and 'drain' and create dense, stackable arrays of nanometer-sized devices which could provide record-breaking data storage densities. Depending on how the materials' magnetic and electrical properties interact, multiple bits of information might even be stored simultaneously. These new materials are expected to be both robust and compatible with existing nitride processing technology, making them of great practical value. Firstly, however, their fundamental properties must be understood more fully, in order to make the most of the fascinating new possibilities they offer for the energy-efficient devices of the future. This can be done by creating and characterising the most promising materials (starting with the (Sc,In,Ga)N materials system), understanding and controlling their fundamental properties and using this knowledge to design new energy-efficient devices that best exploit these properties. Impact: Better green LEDs could help save up to 80% of the energy we use in lighting. Along with more efficient high-power transistors for industry, transport and communications, this would reduce our dependence on fossil fuels significantly. In the long term, such energy-efficient displays and power supplies could also be combined with ultra-high-density memory to give us smaller, faster, lighter computers with enormous data storage capacities and very long battery lives, benefiting almost every part of society.

Successful development of new (Sc,In,Ga)N materials should lead to high-performance green light-emitting diodes (LEDs), new efficient transistor designs and new forms of ultra-high-density data storage, while laying the groundwork for others to develop compact, high-efficiency green lasers, high-efficiency 'concentrator' solar cells and even on-chip cooling devices based on this materials system. In addition to enabling energy-efficient white lighting, efficient green LEDs would facilitate brighter displays with better colour rendering and reduced power usage. High-power transistors would cut the power consumption of motors in transport, appliances and industry, while opening new avenues towards powerful wireless communication and THz scanning technologiees. High-density data storage with rapid data access would lead to smaller, faster, cheaper memory which can cut server and PC energy demands. Efficient green lasers would enable miniaturised projection displays for portable devices such as mobile phones and PDAs, while ultra-efficient solar cells would find use in satellite and space exploration applications and enable grid-independent portable electronics. On-chip cooling devices would also enable laptops free of bulky, power-hungry cooling fans. These improved devices could lead to a total reduction of over 20% in the UK's electricity usage. Benefits to industry: The large number of commercially relevant applications means that a very wide sector of industry stands to benefit from this work, once appropriate high-performance (Sc,In,Ga)N materials have been developed. To ensure this happens, I plan to use our knowledge of (Sc,In,Ga)N materials to design device structures, with the aim of submitting patent applications, assisted by Cambridge University Enterprise (CUE). The high degree of novelty means that valuable 'cornerstone' patents are likely to be obtained. As green-emitting optoelectronics will be developed first, my short-term plans include interaction with and IP licensing or sale to existing collaborators Sharp Laboratories Europe (green lasers and displays) and Philips Lumileds (high-power green LEDs for lighting), thus ensuring rapid commercialisation of technology in this fast-paced area. Later, IP relating to transistors, memory elements or other devices can be exploited via industrial partners reached through CUE, such as companies from the local Cambridge technology cluster. If feasible, I will apply to the EPSRC Follow-on Fund or the Brian Mercer Feasibility Award scheme towards the end of this fellowship to support the feasibility studies needed to acquire venture capital and set up a spin-off company (likely involving fab-less manufacturing). These plans would increase revenue for industry in the long term, whilst I will also contribute in the short term by training highly-qualified students to work in this high-tech sector. On a wider scale, energy-intensive industries such as construction, manufacturing and transport would ultimately benefit from lower overheads resulting from the use of energy-efficient motors and lighting. Benefits to policy-makers: This work is intended to lead to 'green' technology that will help the UK Government reach its legally binding target of a 20% reduction in CO2 emissions by 2020 and reduce our dependence on foreign energy supplies: a cost-effective and widely acceptable way to tackle current concerns over climate change and terrorism. The transfer of cheap energy-efficient technology to developing countries will also allow the UK to contribute towards the Millennium Development Goals. Benefits to the public: The energy-efficient lighting and power-saving electronic technology that should ultimately arise from this work would reduce electricity bills for the public and allow them to benefit from cheaper, lighter and smaller portable electronics and computing and from improved scientific education and awareness as a result of my outreach activities.