Numerical Simulation Of Micro-pulling-down Crystal Growth

Micro-pulling-down method is one of the techniques for producing crystals fiberwith features of growing fast, controlling easily crystal shape. Some specialproperties of crystals can be achieved by adding dopants during its growth, which havea big influence on the performance of the crystal. To improve the quality of thegrowing crystal requires a uniform dopant distribution. However, the convectionstructure in crystal growthand dopant segregation had a bad effect on it. It is importantto investigate the distribution of the dopant and its improving technique for evendopant distribution.The distribution of Dopant Ce in yttrium aluminum garnet(YAG) via themicro-pulling-down method is investigated in this research, and multiple improvingmodels are proposed, which are numerically simulated with the finite volume method(FVM).Firstly, the crystal growth model is established, including concentration boundaryconditions for dopant segregation, then the velocity field, temperature field andconcentration field in the melt arenumerical simulated using the FVM and analysized.Based on this, a crucible with a dip micro-channel improvement model is proposed toimprove the uniformity of radial distribution of dopant Ce, as well, the appropriatephyscial and mathematical model is established to numerical simulation andverification. the radial concentration distribution of dopant Ce in models with differentdip angels are studied, and the radial distribution uniformity is contrasted.Then, the multiinlet models are proposed as follows: five-hole inlet model,nine-hole inlet model and nine-hole staggered inlet model,which is based on thethoughts of increasing the number of micro-channel and changing their positionarrangement to improve the radial distribution of dopant. Select the eighth ofgeometric area for its symmetry of the geometry for numerical simulation to improvethe efficiency of calculation, and the radial dopant distribution on solid-liquid interfaceof each models is studied.At last, The influence of the height of liquid bridge on the uniformity of radialdopant distribution on solid-liquid interface is investigated through numericalsimulation by changing the floating zone height. The results show that:(1) the distribution of dopant along the radial direction isuneven in the process of the micro-pulling down method for crystal growth. The dipangle model can improve this problem and the larger the inclination, the more obviousimprovement.(2) Comparing the uniformity of five-hole inlet model, nine-hole inletmodel with the original model, the nine-hole inlet model is the optimal model.(3)Changing the inlet hole layout position of nine-hole model, the nine-hole inlet model isbetter than nine-hole staggered inlet model.(4) Increasing the height of the liquidbridge can improve the uneven distribution of the dopant in the solid-liquid interface ina certain extant.