NEW SCIENTIFIC KNOWLEDGE ON THE PROCESSES ACCOMPANYING DIRECTIONAL CRYSTALLIZATION OF MELTS AS A RESULT OF EXPERIMENTS ON SEMICONDUCTOR CRYSTAL GROWTH ONBOARD SPACE VEHICLES

摘要

The analysis of experimental results on the studies of components segregation in semiconductor crystals, grown by various directional crystallization methods from the melts in space, is given. The information on quasi-stationary residual microaccelerations onboard space vehicles and also on the results of numerical simulation of heat/mass transfer processes in melts during directional crystallization in microgravity is engaged. It is shown that even small magnitude residual microaccelerations influence the segregation, and it is a manifestation of fundamental hydrodynamic effects of convection, which consist of an origin of concentration and/or temperature inhomogeneities in the melt. To obtain the homogeneous semiconductor crystals by directional crystallization on spacecraft is possible, if intensity of convective flows in the melt is characterized with Rayleigh number no more than 0.01. In this case, as it is expected, the diffusion mechanism of heat/mass transfer will predominate and there will be no mentioned hydrodynamic effects. Some problems on further research including ground based investigations are considered.