Anisotropic Three-Dimensional Thermal Stress Modeling and Simulation of Homoepitaxial AlN Single Crystal Growth by the Physical Vapor Transport Method

Abstract

We develop a thermal-elastic stress model using the finite element method to predict three-dimensional anisotropic stress in AlN single crystals homoepitaxially grown by the physical vapor transport process; we also perform numerical experiments for a 1-in. AlN crystal surrounded by different cone-tube designs and grown along various orientations. The influences of the cone-tube shape and the growth orientation on the stresses inside the AlN crystal are investigated in detail. The simulation results show that the von Mises stress exceeds 1.11 GPa under all specified growth conditions, while the anisotropy is negligible. The resolved shear stresses are strongly dependent on the thermal gradient inside the growing crystal and the growth orientation. Strong anisotropy of the resolved shear stress is observed upon tilting of the growth orientation. The resolved shear stress along {0001}⟨112̅0⟩ primary slip system reveals that the c-axis growing crystal is under tensile stress along all three primary slip directions. Nevertheless, an inversion of the resolved shear stress from tensile to compressive along the −a 3 slip direction is observed when changing the growth orientation. The total resolved shear stress shows 6-fold symmetry, reflection symmetry and 2-fold symmetry along [001], [10√3], and [100] growth orientations, respectively.

Characterization of 60 mm AlN Single Crystal Wafers Grown by the Physical Vapor Transport Method

“…tungsten crucible and two resistive heaters. The hot zone and growth conditions of the growth reactor were optimized by the FEMAG two‐dimensional (2D) global heat transfer model together with our in‐house 2D mass transport and three‐dimensional (3D) stress prediction modules . Details of the AlN boule growth process are not the topic of this work and will be described elsewhere.…”

The Physical Vapor Transport Method for Bulk AlN Crystal Growth

“…Furthermore, the defect generation such as dislocation and small angle grain boundary (LAGB) during growth is significantly influenced by the temperature gradient. Except for the axial temperature gradient, an appropriate radial temperature gradient around the growing AlN crystal can also improve the crystal quality by suppressing the polycrystalline nucleation and reducing the thermal-elastic stresses in crystals [27].…”

Influence of Different Heater Structures on the Temperature Field of AlN Crystal Growth by Resistance Heating

“…The radio frequency induction heating + graphite insulation system uses graphite felt as insulation material. It is reported that C impurity usually exists in the form of CN in AlN crystals, and thus it is easy to form an ultraviolet absorption peak at about 265 nm (4.7 eV) [ 15 ]. The resistance heating + tungsten and molybdenum insulation system has very little C impurity content, and the O impurity content can be further reduced by improving the raw material sintering process, so it is easy to grow AlN crystals with high UV transmittance.…”

“…Q. K. Wang et al simulated the influence of thermal stress and crucible shape on the AlN crystal quality and the transport of vapor species for a resistance heating furnace and found that the distribution and magnitude of stress in AlN crystals are closely related to the temperature gradient and growth direction of the growing crystal [ 15 , 16 ]. The parasitic polycrystalline grains around the crystal are reduced and suppressed by designing different conical confinement rings.…”