Sumathi, R. Radhakrishnan; Barz, Ralph-Uwe; Gigler, Alexander M.; Straubinger, T.; Gille, Peter
Growth of AlN bulk single crystals on 4H-SiC substrates and analyses of their structural quality and growth mode evolution.
In: Physica Status Solidi (A) Applications and Materials Science, Vol. 209, No. 3: pp. 415-418
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Aluminium nitride (AlN) bulk single crystals were grown on off-oriented4H-SiC substrates by the sublimation method. High-quality crystals withabout 25 mm in diameter and up to 5 mm in thickness were obtained withan optimized growth process. The crystals show hexagonal symmetry withwell developed 510 (1) over bar16 side facets. Confocal-Ramanspectroscopy and double-crystal X-ray diffraction rocking curve(DCXRD-RC) measurements confirm the high structural quality of the growncrystals. In Raman spectroscopy, the full-width at half maximum (FWHM)of E-2(high) phonon mode decreases from 40 cm(-1) for thin layers (800mu m) to 22 cm(-1) for a 5 mm thick crystal, showing the improvement inquality with thickness. The DCXRD rocking curve FWHM obtained for a 5mmthick crystal is about 120 arcsec. A basal plane bending of 100 arcsecis observed by rocking curve measurements while scanning 17 mm of thesample’s diameter. Two kinds of growth modes namely, step flow growthand spiral growth modes were observed under similar growth conditions.This may be attributed to a slight variation of super-saturation in thegas phase. In both cases, a single active hexagonal growth centre isformed. As-grown surfaces have been found to be always Al-polar. Wetchemical etching revealed both, threading type and basal-planedislocations (BPD) on the surfaces of the samples with total etch pitdensities (EPDs) in the range of 8 x 10(5)-1 x 10(6) cm(-2). (C) 2011WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim