In this paper a model for thermosolutal convection, thermotransport and mass transport is considered for a Bridgman-Stockbarger growth system. It is shown that if the growth process takes place in zero- gravity or in a low gravity environment and if at the moment when the bottom of the ampoule enters into the gradient zone the dopant concentration in the melt is given by a certain formula, then in the first 70% of the grown crystal the dopant concentration is almost equal to a prescribed concentration. In practice this means that the ampoule has to be filled with thin concentric rings, obtained by compacting powder, each of these rings having a constant concentration of dopant, given by the formula in function of the position of the ring in the ampoule. This ampoule is introduced into the hot zone of the furnace and the content is melted quickly so that the dopant diffusion during the melting process can be neglected. At the end of the melting process the translation of the ampoule begins. Numerical results are given to show the computed improvement obtainable in comparison to the experimental results.
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