Messenger - Vol. 2, No. 1, Page 13
Fall 1992
On the trail of faster, smarter electronics

      Pocket calculators, medical laser devices, automobile ignitions and
the tiny, LED Watchman televisions all rely on semiconductors.
      Semiconductors are materials, like silicon, that can conduct
electricity, though not as well as metals do. They are needed to make
electronic devices such as transistors, integrated circuits and microchips
that are the basis of today's micro-electronic industry.
      "There is an ongoing quest for higher performance from
semiconductors," says James Kolodzey, associate professor of electrical
engineering. "There are groups looking for new structures, different shapes
and sizes, and others looking for better materials. Right now, I am leaning
toward new materials."
      Kolodzey is working at a molecular level to restructure a
silicon-germanium semiconductor that will be useful for smaller, faster and
smarter electronic devices. "Silicon semiconductors are the most common and
pervasive, but silicon cannot easily emit light," he says. "A
gallium-arsenide semiconductor can emit light, but it is difficult to
process, so the search goes on."
      Modern techniques for growing crystals, such as molecular beam
epitaxy, or MBE, make it possible to form new structures and layers in a
semiconductor. "Silicon germanium can be made as an alloy and as layered
structures in which one region has more germanium than another," Kolodzey
says. "These are called hetero-structures, and the MBE process makes it
possible to create light emitters from materials not previously thought
capable of this."
      A silicon-germanium semiconductor would be compatible with the
commonly used silicon, so this combination is promising, he says. However,
sometimes, the electrical/optical properties malfunction because the larger
germanium atom cannot line up with the silicon substrate. "We are trying to
compensate for the strain by adding the diamond form of carbon," Kolodzey
      While on leave in Germany, Kolodzey successfully grew a sample of the
silicon-germanium-carbon alloy using a chemical vapor deposition process,
and its electronic properties were evaluated at Delaware in collaboration
with Mark Barteau and Doug Buttrey in the Department of Chemical
Engineering. The early measurements were encouraging, Kolodzey says, and
were reported at the spring Material Research Society meeting. He expects
to have some results from the MBE process by this fall.
      "Few groups in the world have made this material before, and the
early measurements of properties are encouraging," Kolodzey says. "The idea
may turn out to be a bust, but this type of basic research is always
important. It teaches students how to analyze materials and make new
devices, and future researchers learn what does and what does not work out.
      "On the other hand, if our idea works, this new semiconductor could
result in faster circuitry and improve the performance of high-speed
computers, medical imaging systems and even telephone communications,"
Kolodzey says.
                                   --Cornelia Weil