SiGe crystal growth aboard the international space station

A silicon germanium mixed crystal Si1−xGex (x~0.5) 10mm in diameter and 9.2mm in length was grown by the traveling liquidus-zone (TLZ) method in microgravity by suppressing convection in a melt. Ge concentration of 49.8±2.5 at% has been established for the whole of the grown crystal. Compared with the former space experiment, concentration variation in the axial direction increased from ±1.5 at% to ±2.5 at% although average Ge concentration reached to nearly 50 at%. Excellent radial Ge compositional uniformity 52±0.5 at% was established in the region of 7–9mm growth length, where axial compositional uniformity was also excellent. The single crystalline region is about 5mm in length. The interface shape change from convex to concave is implied from both experimental results and numerical analysis. The possible cause of increase in concentration variation and interface shape change and its relation to the two-dimensional growth model are discussed. •Bulk Si0.5Ge0.5 crystal growth by the traveling liquidus-zone method in microgravity.•Axial compositional fluctuation less than 2.5 at% for 9.2mm length.•Radial compositional fluctuation less than 0.5 at% for 10mm diameter in the region of 7–9mm growth length.•Freezing interface change is discussed in comparison with the measured radial Ge concentration profiles.