Modeling the thermal state of the high-pressure apparatus cell during the growth of gallium nitride crystals

Abstract

Using the finite element method, the thermal state of a specially designed «Toroid-40» high pressure apparatus cell was investigated for conducting experiments on the growth of gallium nitride crystals by the temperature gradient method. The effect of changing the concentration of the composition of the heaters on the thermal state of the high pressure cell was studied. It was determined that the same concentration of graphite in the upper and lower heaters leads to a deviation from the desired horizontal orientation of the temperature isolines in the growth volume. Under the condition that the concentration of graphite in the lower heater is greater than the concentration in the upper one, and this difference exceeds 4 % by mass, the topology of the temperature fields acquires a horizontal orientation, but this leads to an unacceptable increase in the axial temperature gradient. Favourable conditions for the synthesis of GaN crystals (according to the parameters of the gradient and the topology of the temperature isolines) are created under the condition that the concentration of graphite in the lower heater varies in the range of 9–11 %, and in the upper one it is lower by 2–3 % by mass. As a result of the study of the influence of the crystallized GaN phase on the temperature distribution in the Fe–GaN sample, a decrease in the temperature at the control points of the growth volume was obtained (up to 5 °C). The dependence of the maximum temperature difference in the growth volume on the size of the crystallization zone is constructed.

Keywords

• finite element method
• high pressure cell
• high pressure apparatus
• high pressure
• high temperature
• gallium nitride