Wednesday, September 20, 2006

Bringing Light to Silicon

Continued from page 1

By Kate Greene

Finally, metal contacts are connected to the indium phosphide, and an electric current applied. When the current is turned on, negative electrons and their positive counterparts combine within the indium phosphide, explains Bowers, a process that produces photons. These photons are then easily captured and concentrated in the silicon cavity, which emits the beam of light.

The research was funded in part by the Defense Advanced Research Projects Agency, and will appear in an upcoming issue of Optics Express. And it's the most recent advance in a flurry of work out of Intel and its partner universities in the past few years. Last year, for instance, Paniccia's team published three articles in the journal Nature, detailing significant advances in building silicon-based photonic devices (see "Intel's Breakthrough," July 2005).

Other groups are also trying to use well-established silicon processes to put light into computer chips, says Harry Atwater, professor of applied physics and material science at the California Institute of Technology in Pasadena. He and researchers at other institutions, including MIT, are looking to silicon quantum dots for their light-emitting properties, which may eventually be less expensive to manufacture than hybrid lasers using indium phosphide, he says. Indium phosphide, he adds, could still be too expensive for the semiconductor industry to adopt widely. "I'm enthusiastic about [Intel and UCSB's research]," he says, "but [cost is] the thing that tempers my enthusiasm."

He adds that when a company such as Intel finally adopts a process like this in its microprocessor manufacturing plants, "that's the ultimate proof that it's production worthy." Until then, he thinks the researchers have "a long way to go" to demonstrate the cost effectiveness of the technology.

Indeed, Paniccia and Bowers suspect that it could take five years for their device to be incorporated in chip-making facilities. But they're excited by early results, Paniccia says.

His team has already built a laser that emits infrared light with a wavelength of about 1,800 nanometers. The next steps will be to modify the design of the silicon cavity, he says, improve efficiency, and to tune the laser to emit light at many other wavelengths. Simply modifying the cavity to change the properties of the hybrid laser is one example of the benefits to using silicon, says Paniccia. Instead of fabricating a completely different light source, he says, they can just exploit the well-established silicon processes. "It puts all the complexity on the silicon."