Microstructure and strength of AlN–SiC interface studied by synchrotron X-rays

Bulk AlN crystals grown by sublimation on SiC substrates exhibit relatively high dislocation densities. The kind of defect formation at early growth stages influences the structural quality of the grown crystals. In this work, the dislocation distribution near to the interface is understood through investigation of thin (≤1.5 mm) continuous (non-cracked) freestanding crystals obtained in one process with the evaporation of the substrates. The AlN specimens were characterized using synchrotron radiation imaging techniques. We revealed by triple-axis X-ray diffraction study that, near to the former interface, randomly distributed dislocations configured to form boundaries between ∼ 0.02 ∘ misoriented sub-grains (from [0001] direction). Threading dislocation structure similar to that in epitaxial GaN films was not detected. To explain these observations, a theoretical model of misfit stress relaxation near the interface is suggested.