Regulation of the Temperature Field and Evolution of the Melt Convection Field During InP Crystal Growth with the Vertical Gradient Freeze Method

The vertical gradient freeze (VGF) process needs to regulate the temperature field more accurately to ensure the successful seed crystal introduction and good crystal growth condition compared to the vertical Bridgman method, such as a suitable solid-liquid interface temperature gradient. This work presents a method for regulation of the temperature field via temperature control of six heaters during VGF growth of InP crystal with numerical simulation, and shows the involution for both the melt convection and the solid-liquid interface temperature gradient. Two of the six heaters were in the heating zone, two in the gradient zone, and the others in the cooling zone. Firstly, three temperature settings for the six heaters were selected through many trial calculations to ensure the success of seed crystal introduction. Secondly, their effects on the temperature field in the crucible and the convection in the melt were investigated. The results show that the axial temperature gradient in the melt increases with an increase in the heating zone temperature or a decrease in the cooling zone temperature, of which the maximum for each simulation experiment almost always appears at the solid-liquid interface and decreases continuously with the crystal growth process. Moreover, the maximum temperature gradient in the melt for all the simulations is well below 10 K/cm due to the shouldering stage 2, which cannot improve significantly even if the heating zone temperature increases and the cooling zone temperature decreases to room temperature. The temperature setting of the heaters has no significant influence on the convection pattern in the melt, which is nearly the same for all three settings. However, the maximum velocity of the convection field increases significantly with the axial temperature gradient increase. The number of convective vortices in the melt decreases from four at the initial seeding stage to one at the end of the equal-diameter growth for every simulation, but the maximum flow velocity decreases very slowly from the shouldering stage.