Comparison of the Thermal Stress Behavior of AlN Single Crystal Growth on AlN and SiC Seeds via the Physical Vapor Transport Method through Three-Dimensional Numerical Modeling and Simulation

We extend a thermal-elastic stress model by the finite element method to evaluate anisotropic three-dimensional thermal stress in AlN bulk crystals grown on on-axis 2H-AlN and 6H-SiC seeds. The distribution of stresses in the growing AlN crystals at various crystal thicknesses is simulated based on the developed model. The simulation results show that a high von Mises stress layer with strong fluctuations at the 6H-SiC/2H-AlN interface is observed for the heteroepitaxial growth, and a critical crystal thickness of 1 mm for the stress relaxation is required to avoid cracking. On the contrary, a smooth evolution of the von Mises stress is observed for the homoepitaxial growth on the 2H-AlN seed. The maximum total resolved shear stress inside the crystal when using SiC seeds is slightly higher than that of using AlN seeds at the initial growth stage, while this phenomenon reverses after the crystal thickness exceeds approximately 3 mm. Whether using AlN or SiC seeds, the magnitude of the total resolved shear stress increases steadily, and the difference between the homoepitaxial and heteroepitaxial growth is quite small during the whole bulk AlN growth by the physical vapor transport process.

Automated summary

The study on the distribution of stress during growth of AlN crystals using different seeds found that in heteroepitaxial growth, there is a high von Mises stress layer and higher shear stress, requiring a certain crystal thickness to avoid cracking; whereas in homoepitaxial growth, von Mises stress evolves smoothly with slightly lower shear stress. Overall, whether using AlN or SiC seeds, the total shear stress steadily increases in the entire growth process of bulk AlN crystals, with a small difference between homoepitaxial and heteroepitaxial growth.