Numerical modeling of CdTe crystallization from Te solution under terrestrial and microgravity conditions

• Numerical modeling is used to investigate CdTe growth by Traveling Solution Growth.
• A mechanism explaining the growth interface morphological destabilization is proposed.
• Microgravity conditions are favorable for the growth of CdTe with a stable interface.

Numerical modeling is used to investigate CdTe crystallization by Traveling Solution Growth (TSG) technique under terrestrial and microgravity conditions. Numerical results are compared to some experimental observations on CdTe growth by a TSG seeded process under ground conditions. It is found that the instability of the growth interface is related to the compositional non-uniformities of the liquid zone near the solidification front, caused by the species convective transport from the dissolution interface to the growth interface. The modeling of the ground experiment shows a large liquid zone (approx. 5 cm) after the dissolution of CdTe feed material into tellurium. The convection is characterized by a two-cell pattern. The vortex located near the dissolution interface mixes the solute in this region, reducing the tellurium transport to the growth interface. The interface is more stable in this case, but the dopant (indium) distribution is not homogeneous in the solidified sample. Numerical simulations performed by reducing the length of the liquid zone (approx. 2.5 cm) show one single vortex which is extended in the whole melt volume. The intense convection accelerates the tellurium transport to the growth interface, which is destabilized. In order to avoid the morphological destabilization of the growth interface, crucible rotation at constant speed can be applied. In this case, the homogeneity of dopant distribution in the solidified ingots is significantly improved. The modeling of CdTe crystallization under microgravity conditions shows favorable conditions for the growth with a stable interface in the absence of the convection.