Tellurium recrystallization under microgravity conditions and the resulting properties of samples

Three experiments on the tellurium recrystallization by a modified Bridgman method were performed under microgravity conditions on board the Mir orbit al space laboratory using a ChSK-1 Kristallizator furnace. The physical pro perties of samples were studied, including the final crystal structure, the distribution of impurities and defects, and the charge carrier concentrati on and mobility. The results were compared to the analogous parameters of c rystals remelted using the same method under the normal gravity conditions. It is established that the samples recrystallized in a close volume under the on-board microgravity conditions "break off" from the container walls a nd touch the walls only in a few points. This circumstance gives rise to sp ecial effects, such as the growth of crystals with a free surface and deep supercooling. Study of the distribution of electrically active impurities o ver the length of ingots shows evidence of the presence of thermocapillary convective flows in the melt under the microgravity conditions. The flows t end to increase upon separation of the melt from the container walls. The c ontributions due to impurities and electrically active structural defects t o the charge carrier distribution are taken into account. The single-crysta l sample obtained upon the partial recrystallization of tellurium in a clos e container volume under the on-board microgravity conditions exhibits the electrical characteristics comparable to those of a crystal grown by the Cz ochralski technique under the normal gravity conditions. (C) 2000 MAIK "Nau ka/Interperiodica".