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Affordable GaN LEDs target office, home lighting

14 Oct 2014

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Plessey Semiconductors has aimed at producing energy-efficient and low-cost LEDs for home lighting using a technology developed by Cambridge researchers.

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The company is addressing a global market that, according to a report released in 2013 by WinterGreen Research, could be worth up to $42 billion by 2019. Plessey has the ability to manufacture LEDs at a fraction of their costs, using a process developed by Professor Sir Colin Humphreys in the Cambridge Centre for Gallium Nitride.

Blue and white gallium nitride (GaN) LEDs have been commercialised around the world since Shuji Nakamura in Japan developed a method of growing thin GaN layers on sapphire in the early 1990s. Although GaN LEDs are now expected to dominate the world market for lighting, their performance and cost both need to be improved.

Humphreys' team has developed a way of growing GaN on the vastly cheaper substrate silicon and, crucially, a means of scaling this up for commercial purposes. "We've got lower costs for growing GaN LEDs on silicon than anyone else we know," explained Humphreys. "Potentially, this is an advantage that puts Britain right at the forefront of LED research."

Competition between manufacturers (including Toshiba and Samsung) to lead the market in competitively priced LEDs has been intense, driven by the increasing demand for energy-efficient lights.

LED bulbs have much longer working lives than any other forms of artificial lighting: LEDs can last for 100,000 hours compared with 10,000 hours for fluorescent tubes and 1,000 hours for tungsten filament light bulbs. LEDs in dashboards frequently outlive the life of the car; LED light bulbs in the home would probably have to be changed only once in a person's lifetime.

LEDs also use less energy than other forms of lighting. U.K. homes use 20 per cent of their energy on lighting and, because LEDs use 90 per cent less energy than incandescent bulbs, Humphreys estimates that the superior energy efficiency of LEDs could save the $3.2 billion per year in energy, and reduce CO2 emissions.

Humphreys' team has pioneered a technique for depositing successive layers of GaN and indium GaN, each only five to 10 atoms thick and growing at the speed of grass, on a six-inch silicon wafer. The wafer is then cut into 150,000 pieces, each of which forms the heart of a small LED. Using this technology, Plessey hopes to become the commercial leader in GaN-on-silicon LEDs, producing billions per year.

"Growing GaN on silicon is quite a complex process," said Humphreys. A particular problem is the appearance of cracks on cooling from the growth conditions of 1,000°C. This has now been solved by the researchers through careful balancing of the tension in the material as it cools down.

Plessey acquired the technique when it bought the spin-out company CamGaN, set up by Humphreys and colleagues to commercialise the technology. The size of the silicon wafers is greater than the conventional two-inch sapphire wafers, meaning a greater number of LEDs can be made. Fortuitously, Plessey had a six-inch processing line that had been mothballed.


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