Fully-relaxrd n-AlGaN on AlN / Al2O3 templates using strain-relaxed super-lattice buffer layers

Strain relaxation, surface morphology, and threading dislocations of 2.5-mu m-thick n-Al0.6Ga0.4N, grown by metal-organic chemical vapor deposition on AlN/Al2O3 templates using strain relaxed super lattice (SRSL) buffer layers, are investigated. The SRSLs are consisted of 11-115 nm Al0.50Ga0.50N/23 nm Al0.75Ga0.25N multiple layers. The n-Al0.6Ga0.4N layer is fully strain relaxed and smooth surface morphology when grown on the SRSL with Al0.50Ga0.50N thickness over 69 nm. The full width at half maximum values of X-ray rocking curves of n- Al0.6Ga0.4N for (0002) and (1012) planes are 237 and 468 arcsec, respectively. The threading screw dislocations and threading edge dislocations are estimated as 1.2 x 108 cm-2 and 1.1 x 109 cm-2, respectively. The SRSL buffer layer enables to achieve 100% strain relaxation together with a smooth surface and a low threading dislocation density.