Heat and fluid flow in solvothermal autoclave for single-crystal growth process

We report and discuss an experiment and numerical simulation of heat transfer by natural convection inside an autoclave for the solvothermal growth of bulk crystalline GaN. The inner diameter and height of the autoclave were φ 20 and 335 mm, respectively. When the bottom heater of the autoclave is removed and the space between the top and bottom heaters is increased, the crystal growth rate increases. The axisymmetric numerical simulation showed that a rising flow from the center hole in the baffle allows a fast growth rate because the rising fluid is GaN-rich and it reaches the GaN seed crystal quickly. The direction of natural convection can be controlled by changing the vertical position of the heater or baffle.