Growth Kinetics and Thermal Stress in AlN Bulk Crystal Growth

Group III nitrides, such as GaN, AlN and InGaN, have attracted a lot of attention due to the development of blue-green and ultraviolet light emitting diodes (LEDs) and lasers. In this paper, an integrated model has developed based on the conservation of momentum, mass, chemical species and energy together with necessary boundary conditions that account for heterogeneous chemical reactions both at the source and seed surfaces. The simulation results have been compared with temperature measurements for different power levels and flow rates in a reactor specially designed for nitride crystal growth at NCSU. It is evident that the heat power level affects the entire temperature distribution greatly while the flow rate has minor effect on the temperature distribution. The results also show that the overall thermal stress level is higher than the critical resolved shear stress, which means thermal elastic stress can be a major source of dislocation density in the as-grown crystal. The stress level is strongly dependent on the temperature gradient in the as-grown crystal. Results are correlated well with defects showing in an X-ray topograph for the AlN wafer.