The Influence of Thermosolutal Convection on CdTe Growth by the Traveling Heater Method

The effects of natural convection on temperature and solute distributions, growth rate and growth uniformity along the interface are studied for CdTe single crystal growth by the traveling heater method (THM). The study is carried out by developing a thermosolutal convection model to simulate the coupled heat, solute and fluid flow fields in the growth ampoule. The model takes both thermal and solutal convections into account for this material growth and is implemented by the finite element method using the penalty function formulation. Simulation results show that the solute distribution in the liquid zone is significantly influenced by the convective mass transfer and the growth rate increases substantially. This is consistent with experimental observations. The simulations point out the importance of controlling convection for uniform growth. The uniformity of growth along the growing interface is closely related to the effect of the natural convection there. Weaker convection in the interface region is desired for the uniform growth. The heater thermal gradient and the asymmetric distance (offset) between the axial positions of heater peak temperature and solution zone center affect the natural convective state and are investigated through modeling. It is found that a smaller heater thermal gradient and a larger offset moderate the effect of natural convection in the substrate interface region, allowing uniform growth. The model predicts the heater thermal gradient and related growth rate for the crystal growth industry.