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

•Single phase and crack-free (112¯2) AlN layers (~1.1–1.6μm) grown directly on m-plane sapphire substrates by MOVPE.•The layers have mirror-like smooth surface morphology with ~2.5–3.5 nm root-mean square roughness.•Low V/III ratio of 50 was used to reduce the effects of pre-reaction.•Optimal TMAl pre-dose and reactor pressure resulted in the smallest XRC FWHM value of 610 arcsec along [1¯1¯23]AlN and 1480 arcsec along [11¯00]AlN.

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.