Technology to grow GaN substrates may lead to cheaper lighting LEDs
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. They are normally grown on expensive substrates, which pushes up the price of LED luminaires. The new Gallium Nitride growth reactor at Cambridge will allow researchers to improve a method of growing low-cost LED materials on silicon substrates, reducing their cost by more than 50% and opening them up for more general use.
Researchers are developing colour-tunable LED lighting, which would have the quality of natural sunlight, bringing considerable health benefits to users.The same substrates may be sutiable for power-device fabrication and other areas of electronics where power savings are sought.
The reactor, which is funded by the Engineering and Physical Sciences Research Council (EPSRC), was opened on March 28 by David Willetts, the Minister for Universities and Science. It marks the latest chapter in a decade-long research project to make LEDs the automatic choice 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 developed a successful process, and in 2012 this was picked up semiconductor 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 noted for being a more efficient technology for lighting; gallium nitride LEDs 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.”
Making Gallium Nitride LEDs more cost-effective could unlock benefits far beyond energy saving alone. 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.
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, 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.
More information; www.cam.ac.uk/research/news/low-cost-leds-for-saving-energy-and-improving-health
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