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UT Austin scientist builds new semiconductor structures atoms at a time

Dr. Archie Holmes Jr. likes to think small. In fact, he likes to think in microns.

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AUSTIN, TexasDr. Archie Holmes Jr. likes to think small. In fact, he likes to think in microns.

Holmes, an assistant professor of electrical engineering at The University of Texas at Austin, is experimenting with various semiconductor materials — built one layer of atoms at a time. To get an idea exactly how small this is, visualize a human hair. It takes 150 microns, or more than 200,000 layers of atoms, to make up the width of a human hair.

Holmes and his colleagues work in a huge “clean room” at UT Austin’s Microelectronic Research Center, where they develop materials that are used in building complex structures designed to improve the performance of optoelectronic devices.

Holmes’ work with the devices could result in faster Internet access, sharper television images and cheaper, better computers.

“I’m basically developing materials to make communications better,” explained Holmes, who received his bachelor’s degree in electrical and computer engineering from UT Austin in 1991 after graduating from Round Rock High School. He earned master’s and doctoral degrees in electrical and computer engineering from the University of Southern California at Santa Barbara.

Optoelectronic devices have several applications. They include fiber optic communications — everything from telephones to cable television to the Internet, as well as applications involving the emission and detection of light by semiconductors.

Holmes and his colleagues use Molecular Beam Epitaxy (MBE) to fabricate semiconductor structures. MBE creates a low-pressure environment where atoms are focused into a beam and directed toward another piece of semiconductor (called a substrate) that acts as a framework for the construction of semiconductor material structures.

To control the accuracy of the structure, one micron of atoms is laid down per hour onto this framework, eventually building up a crystalline structure. When the crystalline structure is fabricated into a device, it can be used in a system that carries information down an optical fiber via infrared light.

The semiconductor materials that are the focus of the research are gallium arsenide, indium phosphide and nitride-based materials. These materials are capable of emitting light that can carry information farther down an optical fiber before amplification of the light is needed.

The main advantage of fiber optic communications is its ability to carry a thousand times the information of copper wires, still used to carry many of today’s telephone conversations and cable television programs.

Holmes’s research group, teamed with UT Austin electrical engineering professor Dr. Joe Campbell, received international recognition a year ago when they demonstrated the world’s fastest photodetector that operated at a wavelength of 1.55 microns.

The 1.55-micron wavelength represents the wavelength of next-generation fiber-optic communications systems. The significance of this development is that it allows optical fibers in telephone lines to transmit much more information over long distances. At the same time, it maintains truer sounds and images in high-speed data applications such as the Internet.

In January, Holmes’ research group was cited in the American Physical Society’s Physical Review Letters for describing the structure of “quantum dots.” Quantum dots are a special clustering of semiconductor materials believed to offer the speed and cost savings needed for the next generation of fiber optics and computer systems.

These “dots” are far smaller than microns. In fact, they are 20,000 times smaller than the diameter of a human hair. Thus, characterizing, or describing, their shape and positioning required painstaking care and highly sophisticated equipment.

Holmes, whose other “hat” is developing young engineers, has the gift of simplifying the description of his work to its commonly understood use.

“As engineers, we need to share what the benefits of engineering and scientific exploration are,” he said. Holmes said part of that means learning to communicate more effectively about what engineers do, acknowledging that engineering is sometimes hard to explain to those not already in the know.

“My test when I was a graduate student teaching classes was always: ïHow would I explain this to my Mom?’ It’s not a challenge to explain it in esoteric terms, but it is in terms that everyone can understand,” he said.

He currently works with a group of graduate students at the microelectronics lab and teaches junior-level semi-conductor devices classes. “Being a professor was what I always wanted to do,” Holmes said.

Holmes believes engineering is an excellent degree, even if a student eventually plans to go into law or medicine or some other discipline. “The skills that you learn — how to analyze a problem, how to be a part of a team — are valuable in any future endeavor,” he said.

He’s a firm believer that an engineering degree is “about as versatile a degree as you can get. It helps you think critically.” He carries that message to youngsters in public schools, where he extols the virtues of an engineering degree. “I show them a lot of ïwow’ stuff, like the electronic tongue (developed by UT Austin engineers and chemists). It helps get their creative juices flowing and, pretty soon, they’re wondering if an electronic nose would make sense. They begin to see the applications.”

For more information, contact Becky Rische, (512) 471-7272, or the Office of Public Affairs at (512) 471 3151.