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Synchrotron X-Ray Study on Crack Prevention in AlN Crystals Grown on Gradually Decomposing SiC Substrates

We report on the growth method and the structural characterization of freestanding AlN crystals. An AlN layer is grown on a gradually decomposing SiC substrate yielding a freestanding crack free 2H single crystal with dislocation density 5×104 cm–2 and without grain boundaries as confirmed by synchrotron radiation phase contrast imaging and topography data. Wafers of 600–1000 μm thick and up to 15 mm in diameter are obtained. The thermal stress distribution in a conventional AlN/SiC structure is discussed. Theoretical estimates show that cracking of AlN layers is a natural result of their growth on undecomposed SiC substrates.