Structural and surface topography analysis of AlN single crystals grown on 6H–SiC substrates

Bulk AlN single crystals (3 mm thick and 1 in. diameter) were hetero-epitaxially grown on (0001) 6H–SiC substrates by the sublimation method. Double-crystal x-ray diffraction and micro-Raman results confirm the good crystallinity as well as structural homogeneity of the grown crystals. The presence of low-angle grain boundaries was observed by x-ray diffraction rocking curve analysis and also supported by defect-selective etching analysis. The estimated defect density of the 3 mm thick crystals is about (5–8)×105 cm−2. 3D-microstructures with different morphology were observed on the as-grown crystal surfaces and were interpreted to be originated from screw dislocations. These screw dislocations are decorated by carbon impurities as evidenced by micro-Raman spectroscopic measurements. SiC incorporation in the grown crystals was found to be fairly low with 4 mol% at 2 mm distance from the interface and varies slightly between different sub-grains.

► 3 mm thick and 1 in. diameter AlN single crystals were grown on 6H–SiC substrates.
► Quality of grown crystals: DCXRD FWHM ∼120 arcsec Raman E2(high) phonon mode FWHM ∼27 cm−1.
► Total etch pit density of the 3 mm thick crystals is about (5–8)×105 cm−2.
► 3-D growth spirals seen on as-grown surface arise from open-core screw dislocations.
► SiC incorporation is lower (4 mol%) after 2 mm distance from the interface.