[Hicari-II]
Study of Silicon-Germanium Crystal Growth in Microgravity

RESEARCH OVERVIEW

The goals of the Study of Silicon-Germanium Crystal Growth in Microgravity (Hicari-II) investigation are to:

• Observe that Silicon-Germanium (SiGe) crystals have a higher crystal growth rate in space than on Earth. This would mean that a higher temperature gradient on the solid/liquid interface, and/or a higher diffusion constant of the melt, for space grown samples than those grown on Earth.
• Study the more accurate physical properties of SiGe crystals. Highly uniform concentration SiGe crystals grown in the GHF furnace on the International Space Station can help in the develop of growth techniques on Earth, and in the utilization of SiGe crystals in electronic devices.

SPACE APPLICATIONS

SiGe crystals grow faster in space than on Earth and the space station’s Gradient Heating Furnace (GHF) enables highly uniform crystal concentrations. SiGe has been used for thermoelectric devices on deep space exploration spacecraft such as Voyager and New Horizons and improved production could contribute to the development of such devices for future space exploration.

EARTH APPLICATIONS

SiGe crystals are beneficial to infrared (IR) optical lenses and windows because of their non-toxic and flexibility of refractive indices. The use of SiGe in lenses produces a compact, lightweight, high-resolution, and low-cost infrared lens system.

OPERATIONAL REQUIREMENTS AND PROTOCOLS

Ten SiGe crystals are grown over the course of the Hicari-II investigation. Crew members install and remove the metal cartridges, including SiGe crystals, from KOBAIRO rack. The processed cartridges are to returned to the Earth. The experimental conditions are adjusted for future processing runs based on the information gathered from the returned SiGe crystals.

ARAI Yasutomo [JAXA]