TRIPLE-AXIS DIFFRACTOMETRY ON GAN AL2O3(001) AND ALN/AL2O3(001) USINGA PARABOLICALLY CURVED GRADED MULTILAYER AS ANALYZER/

X-ray Bragg diffraction profiles of epitaxial layers of AIN and GaN gr own on c-plane sapphire were measured with a novel triple-axis diffrac tometer using a parabolically curved, graded multilayer mirror in the diffracted beam instead of an analyzer crystal. In addition, the inten sity of the incident beam is enhanced by a parabolically graded multil ayer mirror acting as condenser for a Ge(022) channel-cut monochromato r. This novel diffractometer configuration provides a clear improvemen t in intensity at sufficiently high resolution for the study of angula r peak broadening and peak shape functions of weak reflections from sa mples of poor structural quality and from thin layers. For AIN and GaN , the reason for peak broadening of symmetric rocking curves was found to be small coherence lengths parallel to the substrate surface and n ot distinct out-of-plane misorientations. Additionally, different peak broadenings of asymmetric reflections due to edge dislocations were o bserved for AlN and GaN.