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

摘要

AlN layers were deposited directly on (0001) sapphire by a MOCVD two-step pressure process. The best (0002) and (1012) rocking curves had FWHM values of ～360 arcsec and ～580 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 ω-scans and φ-scans as functions of inclination angle, using the quasi-symmetrical reflection from a group of lattice planes with inclination angle ranging from 0 to 75°. The range of twist spread was found to be sensitive to the substrate nitridation condition. The lowest spread angle obtained with optimized nitridation was ～770 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 Torr, we obtained layers with tilt spreading less than 120 arcsec.