The II-VI semiconductor mercury cadmium telluride, composed of 80 mole percent HgTe and 20 mole percent CdTe, has been grown on Earth and aboard two NASA Space Shuttle flights in order to study the solidification of a solid solution semiconductor having a wide separation between liquidus and solidus. Segregation during solidification, high volatility of mercury, and strain fields associated with large temperature gradients make the growth of homogeneous, high-quality, bulk crystals extremely difficult. The traditional growth methods yield crystals with axial and radial compositional variations and secondary precipitates of tellurium, probably caused by gravityinduced, thermosolutally-driven flows just ahead of the growth interface. The purpose of growing these crystals in microgravity is to reduce gravity-induced convection. This should be advantageous for minimizing the density of crystal defects while also minimizing compositional variation transverse to the crystal growth direction.

The ground based experiments consisted of growing crystals in several different configurations of heat pipe furnaces and NASA’s Advanced Automated Directional Solidification Furnace (AADSF).