Growth of Crack-Free and High-Quality AlGaN with High Al Content Using Epitaxial AlN (0001) Films on Sapphire

High-quality AlGaN with high Al content was grown on high-quality epitaxial AlN film on sapphire (0001) by low-pressure metal organic vapour phase epitaxy (LP-MOVPE). The obtained AlxGa1—xN (0.2 < x < 0.8) thicker than 0.9 μm had atomically smooth surface without any cracks. Full width at half maximum (FWHM) values of X-ray rocking curve (XRC) from the AlGaN were less than 200 arcsec for (0002) diffraction. It is considered that in-plane compressive stress in the AlGaN due to larger in-plane lattice constant of the AlGaN than that of the underlying AlN plays an important role in restraining generation of cracks.