Growing semiconductor crystals in space

Crystals grown in space may hold an important key for the improvement and development of the next generation of computers and communication systems. "Better crystals would improve LEDs, photo detectors, lasers, and wireless devices," says John Walker, a professor of mechanical and industrial engineering at the University of Illinois. He is one of several engineers and scientists working with the Marshall Space Flight Center-NASA's lead center for microgravity research in materials science that is developing alloy crystals. Alloy crystals are blends of germanium and silicon that have highly desirable thermoelectric and electro-optic properties, according to Walker. He explains that NASA, for example, is interested in the crystals for use as solar panels. "The only problem with alloy crystals is that they are so far impossible to grow on Earth because of the effects of gravity. Germanium generally sinks to the bottom of the melt in the crucible because it's three time heavier than silicon," explains Walker. He says that gravity destroys the homogeneous concentration in the crystal. "On Earth, gravity presses the liquid against the walls of the container, resulting in the formation of faults, dislocations, and contact stresses in the growing crystal." The ingredients do not separate in the absence of gravity, which is why Walker proposes growing the crystals on the International Space Station. The pencil-thin crystals would be grown in special ampules within the magnetic damping furnaces on the space station. Walker wants to reproduce them on Earth. Contact Walker at (217) 333-7979.