WASHINGTON, D.C. -- Although it may defy common sense, adding imperfections to materials can actually improve their performance in devices used for everything from information technology to playing music. In this special section, four articles and a special news section show how purposely creating "defects"--or putting naturally occurring defects to good use--can have major implications for the future of electronics and materials science.
The use of semiconductor devices, which allow the manipulation of electric current, has revolutionized information and communications technology. These devices are actually created by introducing impurities into specific regions of a semiconducting material, allowing researchers to control the current in a number of ways, including amplifying it or changing its direction. New applications for defects in semiconductors are being rapidly developed, but scientists do not yet have a thorough understanding of how some defects operate. While semiconductors are best known for their use in computer chips, defects also appear to be useful for improving high-speed communications technology through the engineering of a certain variety of optical fibers.
In one article, Hans J. Queisser and Eugene E. Haller review several of the major ways in which defects affect the performance of semiconductors. In some cases researchers grow pure semiconductor crystals and then "dope" them with foreign atoms. Alternatively, some defects occur naturally within a semiconductor crystal, and researchers must use their ingenuity to find ways of controlling, or even exploiting, these defects.
H. Ohno discusses advances made in merging the capabilities of non-magnetic semiconductors, like silicon, with those of magnetic materials (used to store massive amounts of information; for example, on hard disks). The results could be used to engineer instruments that could perform mass storage and process information at the same time. Ohno shows how researchers have magnetized a non-magnetic semiconductor by adding a magnetic element (technically an "impurity") to the material.
Shuji Nakamura describes breakthroughs in developing a type of "light-emitting diode" (LED) that takes advantage of certain semiconductor defects. An LED gives off light when electric current flows through it. Both CD players and communications systems involving optical fibers use LEDs. However, applications for LEDs have been limited because, until recently there were few materials that emit blue light efficiently. For example, a CD player uses a red laser to read information stored in tiny crevices on the surface of a CD. A laser with a shorter wavelength (such as blue) could access smaller crevices, so that a CD could hold several times as much information. The author reports on progress in creating LEDs that emit blue light.
Demand is quickly increasing for powerful communications media that can transmit information very high rates, or "bandwidth capacities." Currently, information travels through glass optical fibers in the form of light waves. A. F. Garito and colleagues summarize their own progress in improving bandwidth capacities in settings where the fibers must bend and turn sharply--such as an office--by substituting plastic optical fibers for glass. In this case, minute defects in the optical fibers helped coordinate the signals as they traveled, which increased the fibers' bandwidth capacity.
The special issue also includes a news section with articles on carbon nanotubes (strong, flexible, and versatile cousins to the molecules known as fullerenes, or "buckyballs") and the role that defects play when materials crack.
Science is published by the American Association for the Advancement of Science (AAAS). Founded in 1848, the AAAS is the world's largest general scientific society, with more than 143,000 individual members and 280 affiliated organizations. It conducts a variety of meetings and programs in science education and career development, science policy and international scientific cooperation. The Association also produces EurekAlert! (www.eurekalert.org), an online news service featuring the latest discoveries in science, medicine, and technology.
"Defects in Semiconductors: Some Fatal, Some Vital" by H. J. Queisser and E. E. Haller at U. of California and Lawrence Berkeley National Laboratory in Berkeley, CA; H. J. Queisser is on leave from the Max-Planck-Institut für Festkörperforschung in Stuttgart, Germany. CONTACT: Eugene Haller at 510-486-5294 (phone), 510-486-5530 (fax), or firstname.lastname@example.org (e-mail)
"Making Nonmagnetic Semiconductors Ferromagnetic" by H. Ohno at Tohoku U. in Sendai, Japan. CONTACT: Hideo Ohno at 81-22-217-5553 (phone), 81-22-217-5553 (fax), or email@example.com (e-mail)
"The Roles of Structural Imperfections in InGaN-Based Blue Light-Emitting Diodes and Laser Diodes" by S. Nakamura at Nichia Chemical Industries in Tokushima, Japan. CONTACT: Shuiji Nakamura at 81-88-423-7787 (phone), 81-88-423-1802 (fax), or firstname.lastname@example.org (e-mail)
"Effects of Random Perturbations in Plastic Optical Fibers" by A. F. Garito, J. Wang and R. Gao at U. of Pennsylvania in Philadelphia, PA. CONTACT: Anthony Garito at 215-898-5810 (phone), 215-898-2010 (fax), or email@example.com (e-mail)
For copies of the articles in this special section or a copy of the related cover art or additional visual images, please email firstname.lastname@example.org, call 202-326-6440, or fill out the form below in English and fax it to 202-789-0455.
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Defects in Semiconductors: Some Fatal, Some Vital
Making Nonmagnetic Semiconductors Ferromagnetic
The Roles of Structural Imperfections in InGaN-Based Blue Light-Emitting Diodes and Laser Diodes
Effects of Random Perturbations in Plastic Optical Fibers