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Tuesday, August 21, 2007

Simpler white LEDs

Everything from TVs to lightbulbs could be powered more efficiently using white LEDs.

But, since LEDs emit specific colours such as red or green, manufacturers typically have to rely on one or two tricks to produce white light.

One is using the light emitted by a blue or ultraviolet LED to stimulate white phosphorescent dots. The problem with this method is that much of the energy is wasted as heat.

A more efficient method combines the light from red, green and blue LEDs together to form white. But, while blue and green LEDs are simple to create, making red LEDs present a problem.

Red LEDs have to be grown on gallium arsenide wafers which absorb light. So the final stage of their manufacture involves removing the gallium arsenide layer and bonding the diode onto a substrate of transparent gallium phosphide. This significantly adds to the cost and complexity of the process. In addition, red LEDs are not temperature stable and the light they emit changes as they heat up.

Now Charles Tu, an electrical engineer at the University of California San Diego, has come up with a way to grow the LEDs on the transparent gallium phosphide in the first place, significantly reducing cost and complexity and also improving their temperature stability.

Tu and his colleagues say the new LEDs could be used in cellphone displays, computer screens and even in traffic lights.

Read the full patent application for improved red LEDs.

Justin Mullins, New Scientist contributor

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