Improvement of crystal quality of AlN and AlGaN epitaxial layers by controlling the strain with the (AlN/GaN) multi-buffer layer

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 (0 0 0 1) 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 (0 0 0 2) plane (ω scan) and (1 0 1¯ 2) plane (ϕ scan) were decreased from 1530 arcsec to 79 arcsec and 3962 arcsec to 853 arcsec for the AlN template, respectively. FWHM of the ϕ scan XRC was several times larger than that of the ω scan, though the former was roughly proportional to the latter.