Technology bulletin

Efficient LED

The Photon Recycling Semiconductor Light-Emitting Diode (PRS-LED) developed by Fred Schubert, a professor of electrical and computer engineering at Boston University's Photonics Center, is said to be 15 to 20 times more efficient than conventional light bulbs. The PRS-FED may some day replace incandescent, fluorescent, and sodium vapor lights in many applications because it efficiently generates up to 300 lumens per watt. An LED generates light through an electronic process. Electrons enter a light-emitting active region through external wires where the electrical energy of the electrons is transformed into light particles or photons. Unlike other LEDs that have one active region and produce a single color of light, Schubert's PRS-LED uses at least two active regions. The first region converts electrons into photons in the blue range. Some of the photons are directed to the second region which absorbs the light then re-emits it at a different wavelength that produces photons in the yellow-orange-red range. Changing the active regions produces different wavelengths that are configured for producing hundreds of colors, including white light commonly used in homes and public spaces. Schubert indicates that additional potential applications for the PRS-LEDs include signs and displays for automotive dashboards. He also indicated that, although Boston University's primary goal is the education of students, the university is interested in commercialization. "Sure, we are always interested in escaping from the confines of our ivory tower and working with companies," he says. Contact Schubert at (617) 353-1910, fax (617) 353-6440, or e-mail him at efschubert@bu.edu .

Reducing the cost of fiber optics

Peter Esherick is making progress in the task of reducing the high cost of fiber-optic connections. As the manager of the Compound Semiconductor Materials and Processes Department at Sandia National Labs (Albuquerque, NM), he is developing the first 1.3-micron electrically pumped laser that promises to meet the high-speed communications needs fueled by the growing demand for faster Internet access. The vertical cavity surface-emitting laser (VCSEL) that Esherick developed is made mostly from layers of aluminum gallium arsenide and gallium arsenide. An additional ingredient, indium gallium arsenide nitride, causes the VCSEL's operating wavelength to fall into a range that makes it useable in high-speed Internet connections. "We are working with Cielo Communications Inc. (Bloomfield, CO) in a cooperative research and development agreement and they are aggressively pursuing commercialization in telecommunications applications," says Esherick. "However, there may be other applications beyond telecommunications. For example, we are looking at the integration of this technology with microsystems machined from silicon for national security systems," he says. The laser provides a light source that transmits information down optical fibers. In the VCSEL, laser photons bounce between mirrors and are vertically emitted from the wafer surface. "The VCSELs, which are grown by the thousands on a single wafer, are certainly easier to produce than the edge emitter lasers that are currently used," says Esherick. "We expect there to be a great deal of excitement over this product," he says. Contact Esherick at (505) 844-5857 or visit the Sandia National Lab website at www.sandia.gov .

Improving OLED efficiency

Stephen Forrest and collaborators from Princeton University have developed a new cold-welding process for patterning electrodes in OLEDs (Organic LEDs). "A real issue with OLEDs is the ability to pattern quickly without wet chemicals," says Forrest. He believes the new patent-pending process will reduce display-manufacturing costs and make the displays operate with greater efficiency than displays manufactured with other processing techniques. "It only takes us about three minutes to make a display pattern for a cathode," he says. The new process involves pressing a pre-patterned metal-coated stamp onto an unpatterned layer that forms the metal cathode layer of the OLED. Forrest says the process is a little like pulling lint from clothing using a piece of tape. The metal pattern cold-welds to the metal cathode that coats the underlay organic films when pressure is applied to the metal pattern. The next step in the process involves lifting off the cold-welded cathode material from the device, which results in submicrometer feature definition. Contact Forrest at forrest@princeton.edu .