Saturday, January 31, 2009

Cheaper Gallium Nitride LEDs

Gallium Nitride (GaN) LEDs are, in the qualified sense, superior to CFLs. They burn on average 100,000 hours before needing replacement, 10 times longer than compact florescent lamps, and 130 longer than conventional light bulbs; they light up instantly without the warm-up of CFLs; and they contain small amounts of mercury, making their disposal by the well-intentioned but ignorant a bit softer on the environment. The only issue is production cost.

U.K. scientists appear to be on the right path to cheap production enlightenment. According to NewScientist:

The cost of production has kept the LEDs far from homes and offices, however. Gallium nitride cannot be grown on silicon like other solid-state electronic components because it shrinks at twice the rate of silicon as it cools. Crystals of GaN must be grown at 1000°C, so by the time a new LED made on silicon has cooled, it has already cracked, rendering the devices unusable.

One solution is to grow the LEDs on sapphire, which shrinks and cools at much the same rate as GaN. But the expense is too great to be commercially competitive.

Now Colin Humphreys's team at the University of Cambridge has discovered a simple solution to the shrinkage problem.

They included layers of aluminium gallium nitride in their LED design. These layers shrink at a much slower rate during cooling and help to counteract the fast-shrinkage of pure gallium nitride. These LEDs can be grown on silicon as so many other electronics components are. "They still work well as LEDs even with those extra layers inside," says Humphreys.

A 15-centimetre silicon wafer costs just $15 and can accommodate 150,000 LEDs making the cost per unit tiny. That levels the playing field with CFLs, which many people only ever saw as a stopgap solution to the lighting problem.

Commercial availability of LEDs designed by this process may be available within five years.

- Brewskie

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