Growth characteristics of AlN on sapphire substrates by modified migration-enhanced epitaxy

We investigated the effect of growth parameters for obtaining high-quality AlN grown directly on sapphire substrates by a hybridized method, derived from simultaneous source supply and conventional migration-enhanced epitaxy. At an optimal growth temperature of 1200 °C, AlN was atomically smooth and pit-free, while below and above 1200 °C, AlN was rough and with pits, respectively. Surface morphologies also depended on the V/III ratio. Rough surfaces became atomically smooth but then pits appeared, as the V/III ratio increased. The crystallinity revealed by X-ray diffraction changed accordingly. The 600-nm-thick AlN grown under the optimal conditions showed X-ray line widths of as narrow as ∼43 and ∼250 arcsec for (0 0 0 2) and (1 0 1¯ 2) diffractions, respectively.