Convective interaction and flow patterns during oxide crystal growth

Hermann Wilke
Institute of Crystal Growth
Berlin, Germany

Abstract: Oxide single crystals are widely used in laser manufacturing. The Czochralski (CZ) growth of oxide crystals is simulated numerically. During the pulling process the fluid domain occupied by the melt changes its aspect ratio continuously. The laminar melt flow is generated by rotation, buoyancy and thermocapillary forces, respectively. Whereas a changing geometry influences the temperature field and therefore buoyancy and the thermocapillary convection the rotation rate usually remains constant. As a result of this convective interaction complex flow patterns are formed which strongly influence the heat transport in the melt. This is a consequence of the high Prandtl numbers of oxide crystal melts. Using a FEM package the problem can be solved in a 2d axisymmetric geometry. Performing calculations for different aspect ratios by changing the corresponding non-dimensional parameters optimal strategies for the crystal pulling process are predicted.