X-ray characterization of high quality AlN epitaxial layers: effect of growth condition on layer structural properties

AlN layers were deposited directly on (0001) sapphire by a MOCVD two-step pressure process. The best (0002) and (10 (1) over bar2) rocking curves had FWHM values of similar to360 arcsec and similar to580 arcsec respectively. A detailed X-ray diffraction study was carried out to investigate the effect of growth condition on the layer structural properties. In-plane twist was estimated from the FWHM values of both omega-scans and phi-scans as functions of inclination angle, using the quasi-symmetrical reflection from a group of lattice planes with inclination angle ranging from 0 to 75degrees. The range of twist spread was found to be sensitive to the substrate nitridation condition. The lowest spread angle obtained with optimized nitridation was similar to770 arcsec. As expected, the edge-type threading dislocation density estimated from twist spreading was found to correlate well with the dislocation density measured by TEM. The tilt spreading was found to be sensitive to the growth pressure. By reducing growth pressure to 40 Tort, we obtained layers with tilt spreading less than 120 arcsec. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.