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Towards a Silicon Laser

Today¿s most powerful lasers are based on compounds such as gallium arsenide and indium phosphide. But for years researchers have dreamed of coaxing light from another, cheaper material: silicon--the same material from which electronic integrated circuits are carved. A silicon solid state laser would revolutionize information technology, imparting tremendous speed to computers by way of replacing their electrical connections with optical ones. Only one thing has stood in the way of this dream. Normal silicon, it turns out, is not a good emitter of light. Silicon nanocrystals, on the other hand, might be.

According to results described in the November 23 issue of the journal Nature, densely packed nanoparticles of silicon produced a considerable glow when stimulated by pulses of ultraviolet light. Indeed, when Lorenzo Pavesi of the University of Trento in Italy and his colleagues measured the so-called optical gain (when light output exceeds light input), they found that the silicon had yielded values comparable to that from similar arrangements of nanocrystals of compound materials.

The team¿s demonstration of optical gain is an important step toward creating the elusive silicon laser. However, "a true laser has to produce coherent as well as amplified light," Leigh Canham of the Defense Evaluation Research Agency in the U.K. writes in a commentary accompanying the Nature report. "To build a silicon laser, these silicon nanostructures must be made to work inside an optical cavity, in which mirrors can bounce the light back and forth until it becomes coherent," Canham notes. Furthermore, the laser will have to be stimulated electrically rather than optically, as in Pavesi¿s model. Although researchers still have a ways to go before the silicon laser is a reality, Canham predicts that this study will be viewed as a milestone in attempts to develop it. "It appears that we can still teach the ¿old dog¿ of semiconductors a few tricks," he remarks. "It just needs to be restructured on the nanoscale."

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