AlN and AlGaN epitaxial layers with Al composition of 0.6-0.8 were grown by low-pressure metal organic vapor phase epitaxy on a (0001) 6H-SiC substrate using the (AlN/GaN) multi-buffer layer structure (MBLS). Strain of the grown layer could be controlled by structure of the inserted (AlN/GaN) MBLS. It was found that the crystal quality of the grown layer could be improved with increase of the tensile strain in a-axis (compressive strain in c-axis): full-width at half-maximum (FWHM) of X-ray rocking curves (XRC) of both (0002) plane (omega scan) and (10 (1) over bar2) plane (phi scan) were decreased from 1530 arcsec to 79 arcsec and 3962 arcsec to 853 arcsec for the AIN template, respectively. FWHM of the phi scan XRC was several times larger than that of the omega scan, though the former was roughly proportional to the latter. (c) 2006 Elsevier B.V. All rights reserved.