Solidification of Anisotropic Semiconducting Material - Tellurium under Microgravity Conditions

The space flight program for investigation of the action of microgravity on directional crystallization and electrophysical properties of tellurium which is an elementary semiconductor possessing both the anisotropic crystal lattice and energy spectrum was developed and partiy realised Recently three experiments on tellurium recrystallization in space have been successfully carried out using the modified Bridgman method in the Crystallizator CSK-1 furnace on board the MIR space station The crystal structure, charge carrier concentration and mobility, and lattice defect distribution along the samples were studied and compared with those for the crystals grown on earth The results of directional solidification of molten tellurium in microgravity showed the recrystallized samples contacted with the container walls only in a few points: the measured distribution of electrically active dopants and defects along the Te crystals differed from that of the samples grown on earth. The galvanomagnetic measurements allow to separate contributions of impurities and structural defects and to determine the distribution of the electrically active dopants along the samples with the concentration 10 -5 at. %; the charge carrier profile along a crystal depends on the contributions of the impurity (usually traces of Sb) and the electrically active intrinsic defects in the case of partial recrystallization the grown single crystal has the electrical characteristics comparable with the on-ground one, grown by Czochralski method, in the case of entire recrystallization of an ingot the deep undercooling of the Te melt was realised.