Today's silicon-based electronics have a built-in limitation: They fail to function above about 350°C. That limits their usefulness in hot spots, like inside jet or car engines. Now there's a way to grow silicon carbide (SiC) crystals that should handle the heat much better.
SiC is a promising material. SiC devices can operate when glowing red hot--at up to 650°C--reducing the need for coolant systems and potentially resulting in dramatic size and weight savings for aircraft and spacecraft. SiC devices can also carry higher currents than their silicon counterparts, which could lead to higher efficiency electric cars and power networks. Unfortunately, so far SiC crystals have been too unreliable and inefficient to work as building blocks for many devices. That's because the only way to grow SiC crystals--by sublimating vapor onto a crystal seed--creates up to 10,000 structural faults per square centimeter.
To try to reduce the number of faults, materials scientist Daisuke Nakamura of Toyota Central R&D Labs in Aichi, Japan, and colleagues made a key change. To grow SiC crystals, silicon and carbon are stacked in layers, giving such crystals two kinds of faces: c-faces, which are either all carbon or all silicon, and a-faces, which present a mix. SiC crystals are typically grown from the c-faces of seed crystals, but Nakamura and colleagues tried growing them from the a-face instead.
Their new method, described in the 26 August issue of Nature, adds a further twist. First, SiC is grown on an a-face of a seed. The resulting crystal is rotated 90 degrees, and new SiC is grown on its new a-face. The researchers discovered that defects tended to run parallel to the direction of a-face growth, so rotating the crystal presents an a-face with fewer defects, such that crystals grown on it are purer. A final step of c-face growth gets rid of many of the structural defects perpendicular to the direction of growth. All in all, the crystals have 100- to 1000-fold fewer structural defects than those made using the standard technique.
"This is one of the most exciting things that has happened in the last few years," says physicist Erik Janzén of Linköping University in Sweden. He notes, however, that additional studies will be required to see if SiC devices built with these crystals actually do degrade less when used.