SiGe Crystal Growth by the Traveling Liquidus-Zone Method aboard the International Space Station

Abstract

Total of four SiGe crystal growth experiments aboard the ISS were successfully performed for evaluating a two-dimensional growth model of the traveling liquidus zone (TLZ) method and for obtaining insights into large homogeneous SiGe crystal growth conditions. The TLZ growth requires diffusion limited mass transport in a melt and experiments in microgravity are essential. Although a little deviation from the expected compositional uniformity due to emissivity change of the cartridge surface is observed, homogeneous SiGe crystals are grown. Over all axial growth rate is consistent with the one-dimensional TLZ growth model prediction. However, radial growth rates are different from the two-dimensional growth model prediction. The difference is closely related to the flat interface shape in space grown crystals compared with the terrestrial ones and the radial compositional uniformity is much better than those of terrestrially grown crystals. Suppression of convection in a melt is favorable for obtaining flat freezing interface and is beneficial to large homogeneous SiGe crystal growth. It is expected that the obtained results are utilized and large homogeneous crystal growth is realized on the ground and electronic devices using SiGe substrates are developed.