Plastic stretches transistor science.

Plastic stretches transistor science

Traditional semiconductors are made of inorganic materials such as silicon or germanium, but for nearly a decade, researchers have tried crafting semiconductors from organic polymers -- the family of carbon-based materials that includes vinyl. British scientists now say they have manufactured polymer diodes and transistors that are superior in several ways to any built of polymer before. Moreover, they say, the devices eventually might double as elements for computers that use light in addition to electricity to compute.

The transistors and diodes are fashioned out of a stretchy material called polyacetylene, a collection of long, zigzagging chains of carbon atoms. Semiconductors have been made from polyacetylene before, but the newly manufactured devices are better at directing electrons -- up to "three orders of magnitude better" -- and have some novel properties that seem useful, report Jeremy Burroughes, Carole Jones and Richard Friend of Cavendish Laboratory in Cambridge, England, in the Sept. 8 NATURE.

Usually polyacetylene semiconductors, like traditional semiconductors, need to be "doped" with impurities in order to conduct electricity. The British scientists, however, have not needed to dope their material because it has picked up some trace impurity in the processing, Friend says. Because of the relative purity of their polyacetylene, the group claims to be able to resolve a controversial question about whether defects in a molecule's electron cloud called "solitons" (SN: 6/11/83, p.378) exists in the polymer, endowing it with its conductive properties. "What we've shown is that you actually get [solitons] in the devices," he says.

Doping can also change polyacetylene's optical properties, so another advantage of not doping the mixture is that optical changes occur only when an electric field is passed through the devices. This ultimately may be useful to create a transistor-like "gate" to steer light in optical computers, Friend says. "But we're some way from that at the moment," and the new semiconductors will be used mostly to further understanding of these materials, he adds.