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24 January, 2006 - 10:37 By Staff Reporter

Cambridge Lab turns up the Brilliance

A laboratory investigating what has been described as "the most important material since silicon" has submitted a £2m grant proposal for research projects including work that could lead to the development of a solar-powered laser that purifies water.Prof Colin Humphreys, an acknowledged global authority on Gallium Nitride (GaN), believes that the project could transform living conditions in the developing world for millions of people.

The multi-million pound funding application to the engineering and physical sciences research council (EPSRC) should secure the Cambridge Centre for Gallium Nitride’s work for around three years.

GaN emits brilliant light and is the key material for next generation high frequency, high power transistors capable of operating at high temperatures.

This property means that GaN devices can handle much higher power and voltage than silicon, and withstand and operate at much higher temperatures. GaN also has unique optoelectronic capabilities that allows devices to emit blue, green and ultraviolet (UV) light. Such lighting consumes a fraction of the electricity of existing, incandesent or fluorescent lighting and could eventually last indefinitely.

The Cambridge team’s work on ‘deep UV’ LEDs has thrown up the possibility of developing water purifying lasers. "We have only just started our work on deep UV, but we have found that if you ‘hit’ GaN at the right wavelength, about 290 nanometres, it kills DNA and RNA, meaning that it can kill all viruses and bacteria.

"This work could clear the path for the development of systems, powered by solar cells, that clean drinking water in the field. Such technology would make a great impact on health in the developing world."

It is one small area of a wider effort underway at Cambridge University, that has the potential to power a ‘green’ revolution and deliver a host of futuristic products.

The material is already being commercially implemented around the world in the form of blue GaN LEDs, which are filtered using a yellow phosphor to emit white light. The blue LEDs are used in super energy efficient traffic lights in cities around the world from New York to Singapore and lights on cars and in aircraft.

But these initial implementations only scratch the surface of GaN’s potential, says Prof Humphreys, and his group are exploring the boudaries, concentrating on green and ultra-violet (UV) light.

The work is under-pinned by a partnership with Thomas Swan Scientific Equipment, based at Buckingway Business Park in Swavesey. TSSE supplied the lab with a £1m MOCVD reactor, used to grow the GaN materials, which is maintained and serviced free of charge. The company’s senior scientist is also seconded to the Centre for about a quarter of the year.

More natural, consumer-friendly white lighting is one of the major prizes being pursued, Prof Humphreys says. But although blue based LEDs are the first to market, its is UV LEDs that provide the best potential for lighting in homes, offices and mission critical environments. Light created by blued LEDs is still too dim, and too far removed from natural sunlight.

Prof Humphreys said: "The goal is to make energy efficient lighting more attractive. By using UV LEDs in conjunction with red, green and blued phosphors we are able to mimic the physical spectrum of sunlight. In addition to the benefits to people’s health, there are also less obvious benefits to advertising agencies,large consumer brands and the retail sector."

GaN lighting is not only far more power efficient than conventional lighting, potentially it is higher in quality, Prof Humphreys believes. For example, merchandise displayed under artificial lighting very often looks completely different in colour in the shop compared to when worn outdoors.

The ‘natural’ properties of the light could even be used to treat seasonal affective disorder or SAD.

One study suggested that commercially attractive white LEDs, if fully implemented, would save up to $115bn per year in electricity in the US alone by 2015, also reducing air pollution and other waste generated by power plants. Prof Humphreys calculations show that countries such as Sweden and the UK would reduce its CO2 emissions from power stations by 15 per cent, if the switch was made.

The Cambridge centre has managed to wring 67 per cent power efficiencies from UV LEDs, the best in the world, and approaching the inflexion point at which it becomes commercially viable. Blue devices, for example, are around 80 per cent efficient, with lighting company, Osram driving many of the recent advances in performance.

The work on green lighting devices, while not enjoying quite the same revolutionary potential as UV, is also progressing well, with Cambridge again leading other institutions around the world in terms of the technology’s performance. Among the possible applications for green GaN devices is a high-powered video projector, able to project an image over vast distances.

Prof Humphreys and his team collaborate with a number of UK SMEs in addition to TSSE, including Forge Europa in Cumbria, Semelab in Lutterworth and Sharp Europe in Oxford. It also works closely with universities: Sheffield Hallam, Manchester and Brunel.

One recent project, in conjunction with Semelab, is for the development of ‘heads-up’ displays, where maps etc are projected transparently onto the windscreens of cars.

• Another of the smaller local companies operating in the area, Cambridge Electron Beam in Toft has managed to increase the lifetime of the heaters it makes for the MOCVD reactors to 8,000 hours, a four-fold improvement in lifetime over recent years.

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