Technology | Apr 03, 2013

Cambridge Invests £1 million to Accelerate GaN-on-Silicon LED Research

Gallium nitride has been described as “the most important semiconductor since silicon” and is used in energy-saving LED lighting. A new £1million growth facility will allow Cambridge researchers to further reduce the cost and improve the efficiency of LEDs, with potentially huge cost-saving implications.

A new facility for growing Gallium Nitride – the key material needed to make energy-saving light-emitting diodes (LEDs) – has opened in Cambridge, enabling researchers to expand and accelerate their pioneering work in the field.

Gallium Nitride LEDs are already used in traffic lights, bicycle lights, televisions, computer screens, car headlamps and other devices, but they are too expensive to be used widely in homes and offices. The main reason for this is that they are normally grown on expensive substrates, which pushes up the price of LED lightbulbs. The new Gallium Nitride growth reactor at Cambridge will allow researchers to further improve a method of growing low-cost LEDs on silicon substrates, reducing their cost by more than 50% and opening them up for more general use.

LED technology is already so energy-efficient that it is estimated that the overall demand for electricity would fall by at least 10% if every home and business in the UK switched to LED lighting. This would save the UK over £2 Billion per year in electricity costs. Further developments planned in the new reactor would result in an additional £1 Billion per year electricity savings.

In addition, researchers are developing colour-tunable LED lighting, which would have the quality of natural sunlight, bringing considerable health benefits to users.

University scientists are also starting to investigate the potential of Gallium Nitride in electronics, which it is thought could have similarly significant energy-saving consequences – perhaps cutting nationwide electricity consumption by a further 9%.

The reactor, which is funded by the Engineering and Physical Sciences Research Council (EPSRC), was opened today (March 28) by David Willetts MP, the Minister for Universities and Science. It marks the latest chapter in a decade-long research project to make LEDs the go-to technology for lighting, led by Professor Sir Colin Humphreys in the University’s Department of Materials Science and Metallurgy.

In 2003, Humphreys and his team began experimenting with the possibility of growing Gallium Nitride (GaN) on silicon instead of costly sapphire and silicon carbide. After years of painstaking research, they finally developed a successful process, and in 2012 this was picked up by the British manufacturer, Plessey, which has already started to manufacture LEDs at its factory in Plymouth, based on the Cambridge technology. Plessey also hired three of Humphreys’ post-doctoral scientists to help transfer the process. It is the first time that LEDs have been manufactured in the UK.

LEDs are a more efficient technology for lighting because they waste less energy as heat. As a result, they need less electricity overall, and this has a knock-on effect for carbon emissions, because nearly all the electricity in the UK is produced by burning fossil fuels.

A traditional tungsten filament lightbulb, for example, is extremely wasteful – converting just 5% of its electricity supply into light. Fluorescent tubes, by contrast, are 25% energy efficient and compact fluorescent lamps (used as low-energy lightbulbs) are 20% efficient. Gallium Nitride LEDs, however, are already 30% energy efficient and 60% efficiency has been achieved in laboratory research.

“At the moment, a 48-watt LED lightbulb, made from GaN on sapphire LEDs, costs about £15,” Humphreys said. “That’s a cost that you make back several times, because the bulbs last for so long, but it is too much to convince most customers to buy them. The research we have already performed on GaN on silicon LEDs, plus that which we will carry out in this new reactor, will mean that soon people will be able to buy an LED bulb for just £3 instead.”

Minister for Universities and Science David Willetts said: "LEDs are highly energy efficient but expensive to produce, meaning their domestic use is limited. This excellent new facility will enable researchers to look at more cost-efficient ways to produce LEDs, saving money and benefitting the environment. It will also help keep the UK research base at the very forefront of advanced materials, which is one of the eight great technologies."

Making Gallium Nitride LEDs more cost-effective could unlock benefits far beyond energy saving alone. Humphreys is investigating the possibility of “smart lighting” - a system in which LED lights coupled to a sensor would be able to switch themselves on and off, or alter their brightness, relative to a user’s presence or levels of natural daylight in a room.

As their use increases, the beams from LEDs could be used to transmit information, for example from traffic lights to cars. “It’s conceivable that the two could be developed to talk to one another,” Humphreys said. “Traffic reports, such as information about a road accident, could be sent to traffic light systems. They could then relay the details to drivers by transmitting it through the headlamps.”

Researchers also believe that LEDs could be used to purify water supplies in the developing world. Deep ultraviolet (UV) radiation kills bacteria and viruses. By putting a ring of ultraviolet LEDs around a water pipe at the point where it enters a home, it might be possible to kill off bacteria in the water as well as other undesirable organisms, such as mosquito larvae.

Further energy-saving with LEDs may also be possible. Humphreys and his team are currently investigating the so-called “green gap” problem which could improve the way in which they make white light. The LEDs currently used to make white light are in fact blue - the colour is changed using a phosphor coating. This phosphor is, however, not completely energy efficient, and a better way of making white light could be by mixing blue, red and green LEDs together instead.

It is estimated that the overall demand for electricity would fall by at least 10% if every home and business in the UK switched to LED lighting

This, however, depends on resolving lower efficiency in green light compared with the other two colours. If this can be addressed, and LEDs made the standard for lighting nationwide, then it is estimated that there would be an additional electricity saving of 5% - on top of the 10% likely to be engendered by switching to LED technology in the first place.

As well as being used to make affordable, efficient LED lighting, researchers believe that Gallium Nitride could also improve the efficiency of “power electronics” - shorthand for a wide range of devices, circuits, and systems that manage electrical energy. Although power electronics are rarely seen, they affect the daily lives of most people. For example, such devices manage the battery lives of mobile phones, maximise the efficiency of transmission lines, regulate the power in washing machines, and are found in computers, cars and aircraft engines, to name but a few.

At the moment, such electronics are made from silicon, but Humphreys argues that they could be made from Gallium Nitride. As with lighting, the use of GaN would improve their energy efficiency. He and colleagues from several other British Universities have just been awarded a grant by the Engineering and Physical Sciences Research Council (EPSRC) to develop and prototype highly efficient, GaN power electronic devices that could underpin new applications in sectors such as the automotive, aerospace, consumer electronics, lighting, healthcare and energy industries.

“If we can replicate these devices with Gallium Nitride electronics, we believe that we could make them 40% more efficient,” he said. “That in itself would translate into a 9% electricity saving in the UK, if applied across the board.”

Source: University of Cambridge