Prismatic Slip in AlN Crystals Grown by PVT

Basal plane slip is the most frequently observed deformation mechanism in hexagonal aluminum nitride (AlN) crystals grown by the physical vapor transport (PVT) method. However, prismatic slip can also take place in such crystals. In this study, slip in the three prismatic slip systems with nonuniform distributions, observed in a commercial 50 mm AlN substrate wafer, was investigated. The nonuniformity was attributed to the distribution of resolved shear stress in each prismatic slip system caused by radial thermal gradients in the growing crystal boule. A radial thermal model was established to quantitively estimate the thermal stress across the area of the crystal boule during PVT growth. The model results correlated well with both the experimental observations and theoretical calculations of the critical resolved shear stress, revealing that radial thermal gradients play a key role in activating prismatic slip during AlN bulk growth.