LED lightbulbs promise a highly efficient, nontoxic, long-lasting alternative to today’s incandescent and halogen lightbulbs. Lighting entire rooms using LEDs has, however, proved both technically challenging and expensive.
Soraa, a startup based in Fremont, California, has developed a new type of LED that it says generates 10 times more light from the same quantity of active material used in other LEDs. The company’s first product is a 12-watt bulb that uses 75 percent less energy than a similarly illuminating 50-watt halogen bulb. Company officials would not disclose the cost of the bulb, but say it will pay for itself in less than one year through energy savings.
LEDs, which contain a semiconducting material that lights up when current passes through it, are commonly used for low-light applications such as illuminating computer screens. They are usually made by growing a thin layer of gallium nitride on top of a sapphire, silicon carbide, or silicon substrate. Soraa takes a different approach. It uses gallium nitride for the substrate. This reduces a mismatch in the crystal structure between the two layers, which causes the performance of LEDs to diminish as current densities increase. By reducing such mismatches, or “dislocations,” by a factor of 1,000, Soraa officials say they can push 10 times more current through a given area of active layer material. The increase in current density results in a tenfold increase in LED brightness.
Gallium nitride is significantly more expensive than either sapphire- or silicon-based materials, but the increased output more than makes up for the added cost, says Soraa CEO Eric Kim. “We have a simple, highly dense light source that reduces system design, making it the most cost-effective light, period,” Kim says.
Other 50-watt-equivalent LED lights typically combine multiple LEDs into a single bulb. The increased brightness of Soraa’s LEDs means it only has to use a single chip or diode.
Soraa’s LEDs could prove to be expensive, however. Colin Humphreys, director of research at the University of Cambridge’s Department of Materials Science and Metallurgy, says growing gallium nitride in bulk is difficult and time-consuming.
“I pay about $30 for a six-inch-diameter silicon wafer or a two-inch-diameter sapphire wafer, and about $500 for a one-inch-diameter gallium nitride wafer,” he says. Humphreys founded CamGaN, a startup developing LEDs that use gallium nitride on a silicon substrate. The company was recently acquired by Plessey Semiconductors. “[Soraa] may well be able to produce gallium-nitride wafers more cheaply, but surely not at the same price as for silicon and sapphire,” he says.
Kim says Soraa has a novel method of fabrication that significantly reduces the cost of gallium nitride production. He adds that the cost of the substrate is only a “single-digit percent” of the total cost of the company’s bulbs. Soraa has received more than $100 million in startup funding and plans to ship its first bulbs for commercial applications by the end of this quarter.
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