Triple-axis diffractometry on GaN/Al2O3(001) and AlN/Al2O3(001) using a parabolically curved graded multilayer as analyzer

X-ray Bragg diffraction profiles of epitaxial layers of A1N and GaN grown onc-plane sapphire were measured with a novel triple-axis diffractometer using a parabolically curved, graded multilayer mirror in the diffracted beam instead of an analyzer crystal. In addition, the intensity of the incident beam is enhanced by a parabolically graded multilayer mirror acting as condensor for a Ge(022) channel-cut monochromator. This novel diffractometer configuration provides a clear improvement in intensity at sufficiently high resolution for the study of angular peak broadening and peak shape functions of weak reflections from samples of poor structural quality and from thin layers. For AlN and GaN, the reason for peak broadening of symmetric rocking curves was found to be small coherence lengths parallel to the substrate surface and not distinct out-of-plane misorientations. Additionally, different peak broadenings of asymmetric reflections due to edge dislocations were observed for AlN and GaN.