Stripping a molecule to gallium arsenide.

Stripping a molecule to gallium arsenide 

The typical process for manufacturing the semiconductor gallium arsenide requires the use of a gallium compound and a highly toxic, arsenic-containing gas at a high temperature. Now a team of chemists has synthesized a molecule that represents a promising step toward an alternative, potentially better way of making gallium arsenide for electronic circuits and other applications. Their new compound contains both gallium and arsenic in the right proportions and reacts in solution at room temperature to produce gallium arsenide particles.

Normally, molecules containing both gallium and arsenic atoms readily form into pairs or short chains, which are too large to vaporize easily. Chemist Klaus H. Theopold and his colleagues at Cornell University in Ithaca, N.Y., solved the problem by surrounding the gallium-arsenic pair of atoms with small molecular groups--cushioning one gallium-arsenic molecule from the effects of its neighbors (see diagram). They report their findings in the July 15 SCIENCE.

The compound, known as an arsinogallane, dissolves easily in organic solvents such as benzene and decomposes slowly when heated above 60[deg.]C or when exposed to air. With a chlorine-containing compound as a catalyst, the arsinogallane reacts with butanol to produce a reddish gallium-arsenide powder, which slowly settles out of solution. Theopold and his team also have succeeded in synthesizing molecules that contain indium and phosphorus and react similarly to produce indium phosphide.

"The molecular chemistry of these things turns out to be quite fascinating," Theopold says. The chemical reaction appears to strip away all the "cushioning" molecular groups surrounding the gallium-arsenic pair. "We might actually be making molecules of gallium arsenide, the small possible fragments of that material," he says. However, these rarely detected units are unstable, and they begin clumping together into larger partcles. Eventually, the clusters become big enough to drop out of solution.

Even if this particular arsinogallane proves of little practical value in semiconductor fabrication, Theopold says, its chemistry points to an intriguing new group of chemical reactions that may have a variety of applications. The reaction may be useful in probing the properties of small atomic clusters.