Study of SiGe Crystal Growth Interface Processed in Microgravity

A Si-1_Ge-x(x) (x similar to 0.5) crystal measuring 10 mm in diameter was grown by the traveling liquidus zone method using the Gradient Heating Furnace aboard the International Space Station. We quantitatively investigated the composition and shape of the crystal/melt interface during growth by analyzing the grown crystal. The growth interface shapes were obtained by tracing the striations that varied as a result of modulation of the interface near the Si seed to a smooth convex shape as the SiGe crystal growth proceeded. We also successfully measured the Ge concentrations on the interface using an electron-probe microanalyzer. Several growth interfaces showed a highly uniform Ge composition within mole fraction +/- 0.0005. Detailed measurements of the shapes and the Ge concentrations on those interfaces revealed that millimeter-scale Ge concentration gradient fluctuations existed for more than 16 h in a nonsteady and unsaturated SiGe melt in front of a crystal growth interface grown under microgravity conditions.