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News

Future of laser is bright blue

Georgia Institute Of Technology : 27 April, 2001  (New Product)
William S. Rees, Jr. imagines a future where we will carry all of the information that we would ever need, our driver's license, credit cards, security codes, even our mother-in-law's phone number, on a CD-like disk the size of a dime. With the same data storage capability that would make this possible, we could also put the entire Library of Congress on a single 12-inch disk. The key to this future is the production of a commercially viable blue laser, what Wired Magazine calls 'the Holy Grail, the closest the semiconductor biz comes to pure sex.'
William S. Rees, Jr. imagines a future where we will carry all of the information that we would ever need, our driver's license, credit cards, security codes, even our mother-in-law's phone number, on a CD-like disk the size of a dime. With the same data storage capability that would make this possible, we could also put the entire Library of Congress on a single 12-inch disk. The key to this future is the production of a commercially viable blue laser, what Wired Magazine calls 'the Holy Grail, the closest the semiconductor biz comes to pure sex.'

The quest for an efficient blue light-emitting device that could be mass manufactured is not new, a slew of universities and private corporations across the globe have tried for years to manufacture one. Some researchers have achieved limited success, but the same critical problems persist: the lifetimes of such devices are too short, their operating temperatures too high, or, in the case of lasers, they can only operate in a pulsed mode. But according to Rees, who directs the Molecular Design Institute at Georgia Tech and holds a joint professorship in the School of Chemistry and Biochemistry and the School of Materials Science and Engineering, a technique called doping will address all of those challenges.

In an article published in the December issue of the journal Advanced Materials for Optics and Electronics, Rees and Oliver Just, a research scientist in the Molecular Design Institute, demonstrated the validity of their site-specific doping technique and chronicled research on several different materials systems over a period of nearly ten years. Recently, Rees was notified that Georgia Tech was granted allowance of all claims on a patent, a rare occurrence in the world of scientific intellectual property, covering this work in the area of semiconductor dopant molecular design.

The magic of blue lies in its wavelength. At around 450 nanometers, blue is shorter than any other color except violet in the visible spectrum. In the case of data storage, this shorter wavelength allows a blue laser to read and write more information by fitting into smaller 'grooves' on an optical disk. A close cousin to the laser, the light-emitting diode, could also have a tremendous impact if made to shine blue. Both lasers and LEDs are constructed with a two-layered semiconducting material that, when a current is passed through it, emits light. The difference is that in a laser, the light is amplified in one direction.

In the U.S., LEDs are most familiar as lights in car spoilers and personal computer on/off buttons. But a blue LED could be combined with the primary colors of red and green to make any other color, including white. Because white LEDs would be up to 12 times more efficient and longer lasting than conventional light bulbs, experts predict that they will revolutionize the industry, eventually replacing most of the bulbs in the world. The Japanese already employ LED traffic lights, and researchers at Sandia National Laboratories and Hewlett-Packard reported that LEDs could represent a global 'cost savings of $100 billion a year . . . and carbon emission reductions of approximately 350 million tons a year (assuming that all the savings come from coal-fired plants).'

'No other major electricity application (motors, heating, refrigeration) represents such a large energy savings potential [as lighting],' they say.

Such economic potential is certainly not lost on Rees. As a materials chemist, however, he also gets visibly excited by the problem solving opportunities that his blue laser research presents. The doping that he refers to is simply the controlled addition of 'impurities' to the semiconductor, which make it a more efficient light emitter. This materials modification is accomplished through a process called chemical vapor deposition. Rees dubs his particular technique 'the world's smallest paintbrush,' because he designs molecules containing atoms of the dopant which he can place both exactly where, and in what concentration, he desires. Whereas other methods 'paint' only what is in the direct line of sight, Rees works in three dimensions and 'gets around the corners, and into all the nooks and crannies.'

The applications of blue optoelectronic devices are not limited to lighting and data storage; potential uses include underwater communication, flat panel display screens, and ultrafine laser printing.

The Molecular Design Institute at Georgia Tech is a multidisciplinary research unit within the College of Sciences funded by the Office of Naval Research and the Georgia Research Alliance. Its purpose is to combine the efforts of chemists, biologists, engineers, materials scientists, and physicists in atomic-scale work with new molecules and materials. MDI's mission also includes the education of graduate students, and for Rees, it presents a special opportunity.

'MDI gives graduate students the chance to conduct research which lies at the intersection of science and engineering, and take advantage of the best of what the Georgia Tech research environment has to offer,' he says. 'Those students are the heart and soul of everything we accomplish. Beyond all of the discussion about future applications of high-tech materials, the students are why I enjoy what I do.'
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