Friday, October 06, 2006

Will Silicon Light Illuminate the Future?

A startup says it can make silicon-based lighting that will compete with conventional incandescent bulbs and existing LED-based lighting.

By Tyler Hamilton

Researchers at a Canadian startup say they've found a way to make low-cost, white-light LEDs that could one day end our addiction to inefficient incandescent bulbs. They claim to have cracked the cost barrier for solid-state lighting by replacing the expensive semiconductors compounds traditionally used in LEDs with low-cost silicon.

"Because it's a silicon-based system, we think [the lighting] will be affordable," says Stephen Naor, chief executive officer of Ottawa-based Group IV Semiconductor (named after silicon's position in the periodic table). "That's critical, because if you don't have affordability, then nobody is going to buy it."

Roughly 60 percent of all lightbulbs in the world are still incandescent--and for good reason: most cost pennies to produce. However, 95 percent of the energy used by these bulbs is wasted as heat. Solid-state lighting is already widely used for specialty applications; LEDs on Christmas tree lights, for example, are based on gallium nitride semiconductors. And experts predict that this technology will be increasingly used for general lighting purposes (see "Turning on LEDs").

But making LEDs using semiconductors based on gallium nitride requires costly manufacturing processes. "The problem is you're using alloys, and there are always impurities. So you have to grow them using very sophisticated gear under ultrahigh vacuum equipment. It's a very costly process," says Sylvain Charbonneau, professor of physics at the University of Ottawa and director of applications technologies at the National Research Council of Canada. Charbonneau is also director of the Canadian Photonics Fabrication Centre, which Group IV will be using to design a prototype of its technology.

Moreover, semiconductors such as gallium nitride are more expensive than silicon, one of the most abundant elements on the planet. Silicon already has a trillion-dollar infrastructure built around it, to support the global electronics industry, and its properties are well researched and thoroughly understood.

"Silicon for electronics is like carbon for organic chemistry," says Moungi Bawendi, professor of chemistry at MIT and an expert on semiconductor nanomaterials. "It's sand--you can't get better than that, so you certainly have a cost advantage if you can base [an LED semiconductor] on silicon."

There's one catch, though: silicon is poor at emitting light. To overcome this, Group IV fabricated a structure in which an electrical current is passed between the top transparent layer of the device and a substrate made of silicon. In-between these two layers is a layer of silicon nanocrystals--quantum dots--that emits the light. When current is applied, the nanocrystal's electrons are energized; once they settle back into their natural state, energy is given off in the form of photons, producing light.

"The final product would definitely compete head-to-head with [conventional] LEDs, but the way of generating the light at the atomic level would be different," explains Ottawa's Charbonneau. "The technology they use is novel."