EFFECT OF THE SOLIDIFICATION FRONT SHAPE ON THE TEMPERATURE DISTRIBUTION IN THE CRYSTAL

The effect of the solid-liquid interface shape on the temperature distribution in a crystal grown from the melt is investigated. The distribution of axial temperature gradients in a growing crystal is obtained by solving the steady state equation of thermal conduction using a computer and from experimental measurements in NaCl crystals pulled from the melt by the Czochralski method. The presence of an axial gradient maximum in the crystal with a convex-towards-the-melt solid-liquid interface and a monotonous decrease of ∂T(r, z)/∂z|r = 0 from a maximal value on the interface boundary is shown to be due to the direction of heat flows and the shape of isotherms whose geometry depends on the heat loss from the side crystal surface. An analysis is carried out of the effect of the phenomena observed on the magnitude of thermal stresses arising in the crystal. The results obtained suggest that the case of a convex-towards-the-melt solid-liquid interface is the least advantageous to grow crystals with a low defect density. © 1979.