A Record-Breaking Feat

The enclosure is glass-walled. Through the glass door a long tube resembling a telescope is visible. A sign on the wall identifies the apparatus as a molecular beam epitaxy machine.

This futuristic setting is in fact the "clean room" at the Weizmann Institute's Joseph H. and Belle R. Braun Center for Submicron Research, where physicists are growing crystals of gallium arsenide.

The Institute team, headed by Prof. Mordehai Heiblum, and including Dr. Vladimir Umansky and doctoral student Rafael de-Picciotto, recently succeeded in growing the world's purest crystal of gallium arsenide, the semiconductor that is gradually replacing silicon, the mainstay of the microelectronics industry, in a variety of applications. For example, the main component of a cellular phone and the laser element in a compact disc player are made of gallium arsenide. This semiconductor is proving to be more efficient in carrying more and faster electronic signals, and it holds up better in outer space, where communications equipment is subjected to very low temperatures and high dosages of radiation.

Purity in semiconductors can be tested in two ways: the number of foreign, or non-gallium arsenide atoms the crystal contains, and the speed at which an electron can pass through it. The Institute team's crystal has only one foreign atom per five billion gallium arsenide atoms. This is the equivalent of a single cube of sugar in a five-story apartment house on a 300-square-meter lot.

As for speed, the new crystal beat the world record set by Bell Laboratories in 1989. Their material logged 11.7 million centimeters per second. Under the same conditions, electrons zoom through the Weizmann Institute crystal at 14.4 million centimeters per second. That's a speed of 518,400 km (324,000 miles) an hour.

What's the significance of these numbers? First, there are the commercial possibilities that producing a pure gallium arsenide crystal may bring. With fewer impurities, electrons will move faster, and this, in turn, will make a device work more quickly and more efficiently. Purity is also essential for manufacturing miniature electronic devices that behave in a predictable and uniform manner, a crucial factor for the electronics industry.

This research also has important implications for mesoscopic physics, the study of the behavior of electrons in very small devices.