Growth kinetics and thermal stress in AlN bulk crystal growth

Group III nitrides, such as GaN, AlN and InGaN, have attracted great attention due to their applications in blue-green and ultraviolet light emitting diodes and lasers. In this paper, an integrated model has been developed based on the conservation of momentum, mass, chemical species and energy together with boundary conditions that account for heterogeneous chemical reactions both at the source and seed surfaces. The predicted temperature profiles have been compared with measurements for different power levels and flow rates in a reactor for AlN crystal growth at the North Carolina State University. We have found that the heat power level affects the entire temperature distribution greatly while the flow rate has insignificant effect on the temperature distribution; the overall thermal stress level is higher than the critical resolved shear stress, indicating that thermal elastic stress can be a major source to induce high 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 plate crystal.