Single phase (112¯2) AlN grown on (101¯0) sapphire by metalorganic vapour phase epitaxy

Heteroepitaxial growth of AlN buffer layers directly on (101¯0) sapphire substrates by metalorganic vapour phase epitaxy has been investigated. A single-step growth procedure without a sapphire nitridation was employed resulting in mirror-like crack free ≈1.1-1.6μm thick AlN layers of single phase (112¯2) orientation. Trimethylaluminum pre-dose time and reactor pressure were optimized for surface roughness and crystal quality. The crystal quality was found to degrade with increasing pre-dose time and also reactor pressure. The smallest full width at half maximum value for on-axis X-ray rocking curve of the (112¯2) AlN layers was about 610 arcsec and 1480 arcsec along [1¯1¯23]_AlN and [11¯00]_AlN, respectively. The surface roughness, measured by atomic force microscopy using a 10×10μm² area, was in the range 2.6-3.5 nm. A basal stacking fault density of (7±1)×10⁵ cm^-1 was estimated by transmission electron microscopy.