High quality 10.6 μm AlN grown on pyramidal patterned sapphire substrate by MOCVD

In this letter, we demonstrate a crack and strain free AlN epilayer with a thickness of 10.6 μm grown on a pyramidal patterned sapphire substrate by metalorganic chemical vapor deposition. The full width at half maximum of the X-ray rocking curve was 165/185 arcsec for (002)/(102) planes, respectively. The total threading dislocation density was less than 3  × 108 cm−2. The dislocation evolution and the coalescence process were probed by transmission electron microscopy and scanning electron microscopy. A dual coalescence of the AlN epilayer was observed, which can effectively relax strain during the heteroepitaxy process. Owing to the approximately entire strain relaxation demonstrated by reciprocal space mapping and Raman shift, the surface morphology was crack-free and atomically smooth with a root-mean-square roughness of 0.14 nm. Temperature dependent Raman spectra showed the Raman linewidth of 4.3 cm−1 at 300 K which was comparable to that of bulk AlN; it also demonstrated good crystalline quality o...