Homogeneous SiGe crystal growth in microgravity by the travelling liquidus-zone method

Homogeneous SiGe crystal growth experiments will be performed on board the ISS "Kibo" using a gradient heating furnace (GHF). A new crystal growth method invented for growing homogeneous mixed crystals named "travelling liquidus-zone (TLZ) method" is evaluated by the growth of Si_0.5Ge_0.5 crystals in space. We have already succeeded in growing homogeneous 2mm diameter Si_0.5Ge_0.5 crystals on the ground but large diameter homogeneous crystals are difficult to be grown due to convection in a melt. In microgravity, larger diameter crystals can be grown with suppressing convection. Radial concentration profiles as well as axial profiles in microgravity grown crystals will be measured and will be compared with our two-dimensional TLZ growth model equation and compositional variation is analyzed. Results are beneficial for growing large diameter mixed crystals by the TLZ method on the ground. Here, we report on the principle of the TLZ method for homogeneous crystal growth, results of preparatory experiments on the ground and plan for microgravity experiments.