Anomalous effects in dopant distribution in Ge single crystals grown by the floating zone technique aboard spacecrafts

Specific features of Ga-dopant distribution in Ge single crystals grown by the floating zone technique from lightly and heavily Ga-doped Ge melts aboard the Photon spacecrafts have been studied. An anomalously strong concentration dependence of the effective coefficient of Ga distribution in Ge crystallized from melts with a well-developed free surface, which has no analogues under the terrestrial conditions, has been established for the first time. This anomaly is interpreted as a consequence of specific concentration-dependent processes of heat and mass transfer in the molten zone, and, first of all, the intensification of the concentration-capillary convection with an increase of the doping level. The quantitative characteristics of the crystallization parameters necessary for the construction and verification of hydrodynamic models are obtained experimentally. The effect of the observed phenomena on the electrophysical homogeneity of the grown single crystals and possible methods for the control of dopant distribution in such crystals are discussed.