| A Material World: | |
| Materials Chemistry and Physics | |
Because they glow without any increase in temperature, phosphors are an important and highly researched area for numerous emerging flat panel display technologies. Much of that research is under way at the Phosphor Technology Center of Excellence (PTCOE), a multi-university research effort headquartered at Georgia Tech and directed by materials scientist/engineer Dr. Chris Summers.
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PTCOE researchers are studying improved low-voltage, thin-film electro-luminescent displays, field emission display films and thin-film cathode ray tube films.
The research, funded by the Defense Advanced Research Projects Agency (DARPA), is aimed at developing novel phosphor materials and structures for these applications. Already, researchers have made significant progress toward development of a new phosphor material for use as a blue emitter. The material could also be used for electro-luminescent displays in developing low-temperature processing techniques that will enable low-cost manufacturing on glass substrates.
In addition, new phosphor coating techniques are showing promise for improving the performance of low-voltage phosphors for field emission displays, an important first step in reducing their power consumption.
Meanwhile, chemist Dr. William Rees is clearing a significant fundamental hurdle that lies between current electronic device performance and improvements in technology for items such as flat panel displays. That hurdle is rigorous control of dopant element placement in opto-electronic materials. Doping introduces various elements to produce the desired material properties.
Rees is addressing the problem by designing molecules to use as chemical precursors for the doping process. Typically, researchers introduce dopant elements into materials by high-energy ion implantation, a process under thermodynamic control. The technique often creates substantial secondary damage in the structure.
But Rees and his collaborators are developing a class of metal amides as alternative dopant precursors — ones functioning under kinetic control. Rees has demonstrated this process at a lower temperature than is possible with high-energy ion implantation. The researchers have successfully tested the doping process under kinetic control in materials systems including: nitrogen-doped zinc selenide; erbium-doped silicon; and cerium-doped strontium sulphide.
These materials systems are used in blue opto-electronics, silicon-based opto-electronics and blue phosphors for electro-luminesant flat panel displays, respectively.
A materials physics research program is investigating novel material systems created by the metalorganic chemical vapor deposition (MOCVD) technique. MOCVD was developed in the 1960s at TRW and improved at Georgia Tech during the past 15 years. Researchers can fabricate a material system by MOCVD as a single layer or a multi-layer with thicknesses in the atomic scale to obtain material properties that do not exist in nature.
In this study, physicist Dr. Ahmet Erbil hopes to create new material systems for basic research and for electronic and photonic applications by controlling the growth process at the atomic level.
These novel material systems offer a wide range of unique scientific opportunities in condensed matter physics and materials science. Research in these areas also has practical applications in the immediate future, and these material systems probably will form the foundation on which the technology of the next century will rest, Erbil says. For example, he recently demonstrated that when two oxide compounds are deposited in alternation to form a single crystal material system, the dielectric response increases by about a thousand-fold. Because high dielectric response means high charge-holding capacity, the computer memories made from this type of material system can enhance the information storage capacity by the same factor.
Typical devices and applications produced by MOCVD include: high-efficiency solar cells for next-generation satellites; the high-brightness LEDs in all colors of the spectrum that are rapidly replacing incandescent lighting; and as lasers for various uses in communications conduits and in printing, bar-code scanning, and as higher capacity CD-ROMs and DVDs in computers.
— Jane M. Sanders
For more information, contact:
(1) Dr. Chris Summers, School of Materials Science and Engineering, Georgia Tech, Atlanta, GA 30332-0245. (Telephone: 404-894-3420) (E-mail: chris.summers@mse.gatech.edu);
(2) Dr. William Rees, School of Chemistry and Biochemistry, Georgia Tech, Atlanta, GA 30332-0400. (Telephone: 404-894-4049) (E-mail:
will.rees@chemistry.gatech.edu);
(3) Dr. Ahmet Erbil, School of Physics, Georgia Tech, Atlanta, GA 30332-0430. (Telephone: 404-894-6817) (E-mail:
ahmet.erbil@physics.gatech.edu)
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