Detached and Floating-Zone Growth of Semiconductor Crystals on the ISS

Understanding the mechanism of detached Bridgman growth and establishing the growth of large scale germanium-silicon crystals by the float-zone technique are the key points of the project "RDGS - Reduction of Defects in Germanium-Silicon". The contact angle of the melt and the growth angle of the crystal are essential parameters which allow a controlled use of detached growth. The contact angle was determined for a variety of different substrates and melt compositions; pBN showed the highest value for pure germanium as well as for germanium-rich GeSi melts. The growth angle of Ge(sub 0.95) Si(sub 0.05) was measured to be 8.5-10.5 degrees which concurs with the values of pure germanium and silicon, respectively. The temperature dependence and the concentration dependence of the surface tension were determined for concentrations up to 10at% silicon (partial derivative (gamma)/partial derivative T=-0.08 (raised dot) 10(exp -3)N/m (raised dot) K, partial derivative (gamma)/partial derivative (C)=2.2 (raised dot) 10(exp -3)N/m (raised dot) at%). Using these values, the critical Marangoni number indicating the transition to time-dependent thermocapillary flow will be exceeded for the growth of large scale float-zone crystals onboard the ISS. Therefore, suitable tools for flow control are required.