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Scientists had always assumed that the crystal structure of silicon would preclude the development of a directly pumped silicon laser. But, researchers at Brown University have seen the light and discovered that silicon modified at the atomic level can play laser after all, albeit only weakly and then at the extremely chilly temperature of minus 200 Celsius. This first step could lead to silicon LED lasers that might be integrated into microelectronics and microelectromechanical (MEMS) devices for lab-on-chip and other applications. Jimmy Xu and his colleagues have engineered the first directly pumped silicon laser by changing the structure of the silicon crystal at the nanoscale level. Essentially, they drilled billions of tiny holes into a small piece of silicon using a nanoscale template. Coherent light emission from silicon previously seemed unattainable because the electron bandgap is indirect in crystalline silicon making it difficult to emit light. However, silicon is amenable to shaping with microlithographic and other techniques and Xu's colleagues hoped that the right changes to its structure might allow it to emit light nevertheless. The Brown team used a mask of anodized aluminium and bombarded a sliver of silicon with an ion beam to punch out precise but tiny holes in the silicon. The researchers explain their aim was to make the bandgap more direct by shifting the arrangement of atoms around the holes and so allow for light emission. Graduate student, Sylvain Cloutier, tested their meta-silicon over the course of a year to determine its laser properties. The results of edge-emission measurements published in Nature Materials in December demonstrated silicon's threshold behaviour, optical gain, spectral line-width narrowing, cavity modes, and self-collimated and focused light emission. Colleague Pavel Kossyrev repeated and confirmed these results, which all indicate amplification and stimulated emission of light, and laser action in other words. "There is fun in defying conventional wisdom," says Xu, whose Laboratory of Emerging Technologies is drolly known as the Laboratory of "Impossible" Technologies, "and this work definitely goes against conventional wisdom ? including my own." Earlier attempts at producing a silicon laser have involved the production of silicon nanocrystals and other chip manufacturer Intel announced a silicon laser early in 2005. however, this device was a so-called Raman laser making use of silicon as a nonlinear crysal to convert a powerful laser beam at one wavelength into a weak one at a longer wavelength. Related links: |
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