Sumathi, R. Radhakrishnan; Barz, Ralph-Uwe; Gille, Peter; Straubinger, T.
Influence of interface formation on the structural quality of AlN single crystals grown by sublimation method.
In: Physica Status Solidi (C) Current Topics in Solid State Physics, Vol. 8, Nr. 7-8: S. 2107-2109
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AlN single crystals with 25 mm diameter and 3 mm thickness were grown on on-axis, Si-terminated, (001) 6H-SiC substrates with a growth rate of 20-25 μm/h by the sublimation method. The growth conditions were optimised and the grown crystals exhibit good crystalline quality as analysed by double-crystal x-ray diffraction measurements. The FWHM value of the rocking curves in ω-scan is about 100 arcsec for 3 mm thick crystals. The kind of AlN/SiC interface formation influences the structural quality of the grown crystals by forming low-angle grain boundaries. Optical and scanning electron microscopic analyses performed on cross-cut samples demonstrate the existence of an array of hillocks and voids between them at the bottom of the grown AlN layer. These hillocks are confirmed by electron probe micro analysis as SiC etch hillocks and their origin was investigated. The possible mechanism for the formation of low-angle grain boundaries is discussed and a simple physical model is proposed. Optimisation of the growth conditions was carried out in order to obtain crystals with low silicon carbide incorporation.