Global modeling of bulk crystal growth of cadmium zinc telluride in industrial VB/VGF systems

In this thesis, mathematical models and numerical simulations are used to study different aspects of the physics involved in the bulk growth of single crystals of cadmium zinc telluride (CZT) in vertical Bridgman (VB) and vertical gradient freeze (VGF) systems.; A two-dimensional crystal growth model is developed for bulk crystal growth in VB/VGF systems, consisting of conservation equations for coupled bulk transport---heat, momentum, and species transport---thermodynamic relations associated with phase change, along with appropriate boundary conditions and initial conditions. Galerkin finite element method is used to discretize and solve for the spatial part of the governing equations. Implicit time marching schemes are used to solve for the temporal part of the governing equations.; By simulating crystal growth of CZT in an industrial crystal growth system, with this crystal growth model we highlight its limitations vis-a-vis its ability to capture furnace heat transfer effects. Coupling schemes are then developed to link this crystal growth model with a furnace heat transfer model. Using these coupling schemes we obtain a self-consistent solution to CZT growth by accounting for the two-way interaction between the crystal growth domain and the furnace. The performance of these coupling schemes with respect to convergence is investigated as a function of coupling parameters. A systematic procedure to find the regions in the parameter space of the coupling parameters that leads to fast convergence is also developed.; A ternary diffusion model is developed for the species transport in the CZT melt. This model allows for the treatment of cadmium, zinc and tellurium as separate entities in the melt of CZT, unlike the often used pseudobinary diffusion model which treats the melt as a mixture of cadmium telluride and zinc telluride. For a prototypical VB system, transient simulations are conducted using both the diffusion models, and the results from these models are compared with each other. Counter-intuitive zinc composition profiles in the CZT melt are predicted by the ternary diffusion model. Zinc segregation in the crystal predicted by these two models also differ from each other.