Numerical study of ACRT in the THM growth of CdZnTe crystals

Abstract The accelerated crucible rotation technique (ACRT) is a widely used method for the optimization of crystal growth. However, the interactions between the original natural convection in the traveling heater method (THM) and forced convection by ACRT make the flow behavior complicated and also hard to be predicted. With the help of numerical simulation, the effects of different ACRT regimes on flow patterns, growth interface, and temperature gradient during the THM growth are discussed. The simulation results show that there are two kinds of hydrodynamics mechanisms during ACRT, i.e. Ekman flow and centrifugal-force-induced vortex. When a small-rotation ACRT of 2.5 RPM as recommended by classical Ekman flow theory is used, the Ekman flow is too weak to affect the initial natural convection. A counter-rotating vortex arising from the uneven distribution of centrifugal force will be periodically formed in the center, causing a large transient growth rate and a fluctuating temperature gradient. Increasing the rotation rate to 15 RPM, the centrifugal-force-induced vortex disappears and the flow structure is greatly changed under the combined effects of Ekman flow and natural convection. A convex interface is obtained and the transient growth rate is also reduced. Finally, the effect of a large-rotation ACRT of 40 RPM is also discussed.