(a) The six-circle diffractometer at the SCD bending magnet beamline at ANKA (left), showing the linear detector, the crystal analyser and a sample mounted on the Euler cradle stage. The inset shows the layout of the Al0.2Ga0.8N samples. Schematic representations of the coplanar geometry used for symmetric high-resolution X-ray diffraction (middle) and for the noncoplanar GID geometry (right). (b) Reciprocal-space map of the 00.2 reflection with two distinguishable peaks corresponding to AlN and AlGaN (left). The 00.8 reflection (middle) shows two AlGaN peaks, corresponding to the overgrowth layer and to the 150 nm AlGaN interlayer. The GID reflection 10.0 (right). All maps were obtained using sample A4.