Silicon Carbide without Defects

MATERIALS SCIENCE

A long-sought method to grow defect-free silicon carbide (SiC) single crystals for use as semiconductor wafers has been developed by a team of Japanese researchers. The technology advance means that SiC could now begin to be used as a more durable replacement for standard silicon semiconductors in a range of electronic devices for high-power, high-frequency, and high-temperature applications.

Silicon carbide has been studied since the 1950s as a potential replacement for silicon in certain electronic devices. One lingering problem has been that SiC does not have a liquid phase, so the standard technique of controlled solidification of a liquid, used to make silicon and other semiconductors, can’t be used.

Instead, a vapor deposition method in which SiC is sublimed onto a seed crystal is used. But this technique leads to misalignment of some SiC molecular layers, introducing lattice defects that interfere with performance and have limited the material’s use.

Daisuke Nakamura and Kazumasa Takatori at Toyota Central R&D Laboratories in Aichi, Japan, and colleagues there and at DENSO Corp. have now solved this problem by growing SiC in multiple stages [Nature, 430, 1009 (2004)]. The researchers start by growing a SiC layer on a SiC seed crystal. As expected, the growing crystal inherits defects from the seed crystal parallel to the growth direction, a pattern the researchers had previously observed.

To combat propagation of the defects, the scientists stop crystal growth and then restart it on a new crystal face along an axis perpendicular to the original direction. The crystal growth in the new direction inherits fewer defects. By repeating this step-growth process on different perpendicular faces, the researchers gradually obtain crystals with a decreasing number of defects.

The Japanese team can now prepare SiC wafers several centimeters in diameter that have two to three orders of magnitude fewer defects than SiC crystals grown traditionally.

“These substrates will promote the development of high-power SiC devices and reduce energy losses of the resulting electrical systems,” Nakamura says. Potential applications include amplifiers and power converters that operate under extreme or prolonged conditions in jet engines, automobiles, and household appliances, he adds. The SiC technology could be put into practical use by about 2010, Nakamura believes.

“These results are spectacular,” notes physicist Roland Madar of Institut National Polytechnique de Grenoble, in France, in a Nature commentary. The new process is a major innovation in materials science, he says. “Silicon carbide has become, at last, a contender for silicon’s crown.”