Crystal flaws tune the wavelengths. (Light Switch).By exploiting a defect in a semiconductor's crystal structure, researchers have come up with a potentially inexpensive way to make fast fiberoptic communications components. That development, in turn, might speed the long-awaited extension of optical networks into homes, says Janet L. Pan of Yale University Yale University, at New Haven, Conn.; coeducational. Chartered as a collegiate school for men in 1701 largely as a result of the efforts of James Pierpont, it opened at Killingworth (now Clinton) in 1702, moved (1707) to Saybrook (now Old Saybrook), and in 1716 was . Working with gallium arsenide An alloy of gallium and arsenic compound (GaAs) that is used as the base material for chips. Several times faster than silicon, it is used in high frequency applications such as cellphones, DVD players and fiber optics. , the primary material from which lasers for compact-disk players and the high-speed electronics for cell phones are made, Pan and her colleagues have created a light-emitting diode (LED). The device converts electric pulses into light emissions at the pivotal infrared wavelength of 1.55 micrometers ([micro]m), the one used for long-distance optical-fiber communications. Ordinarily, gallium arsenide emits at 0.85 [micro]m. Many manufacturers currently use indium phosphide phosphide Any of a class of chemical compounds in which phosphorous is combined with a metal. Phosphides exhibit a wide variety of chemical and physical properties. Phosphides that are rich in metal have high melting points and are hard, brittle, and chemically inert; these for making LEDs, lasers, photodetectors, and other components of fiberoptic systems. However, for electronics, indium phosphide is difficult to use and leads to many defective components that can't be sold. By contrast, because gallium arsenide parts can be fabricated fab·ri·cate tr.v. fab·ri·cat·ed, fab·ri·cat·ing, fab·ri·cates 1. To make; create. 2. To construct by combining or assembling diverse, typically standardized parts: in the same automated processes that create gallium arsenide-based microelectronics, the new fiberoptic devices may prove to be relatively cheap, Pan says. In the June Nature Materials Nature Materials is a monthly multi-disciplinary journal aimed at bringing together cutting-edge research across the entire spectrum of materials science. The journal’s Impact Factor of 19. , the Yale team explains how it exploited gallium arsenide defects known as arsenic anti-sites. At those locations, the scientists introduced extra arsenic atoms to replace some gallium atoms in the compound's crystal lattice crystal lattice Three-dimensional configuration of points connected by lines used to describe the orderly arrangement of atoms in a crystal. Each point represents one or more atoms in the actual crystal. . In that manner, the team built an LED that contains a layer especially rich in arsenic anti-sites. In LEDs, mobile electrons drop from higher to lower energy levels and fire off photons whose wavelengths correspond to the differences between those levels. In gallium arsenide, anti-sites permit electrons to assume intermediate energy levels that aren't otherwise present. When electrons drop into those middle levels, they emit photons with less energy, and therefore longer wavelengths, than usual. The new LED is "a clever way to make use of a very high concentration of defects," comments David C. Look of Wright State University in Dayton, Ohio Dayton is a city in southwestern Ohio, United States. It is the county seat and largest city of Montgomery County. As of the 2005 census estimate, the population of Dayton was 158,873. . For the moment, Pan notes, the LED's light-producing efficiency is too low to be useful, adding that "practical devices may be possible within 3 to 5 years." |
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