Kinematical and dynamical contrast of dislocations in thick GaN substrates observed by synchrotron-radiation X-ray topography under six-beam diffraction conditions

Dislocations in a thick ammonothermal GaN substrate were investigated by synchrotron-radiation X-ray topography (SR-XRT) performed under six-beam diffraction conditions. The use of high-brilliance synchrotron radiation enabled the observation of the super-Borrmann effect, which significantly enhanced the anomalous transmission of X-rays through the 350-μm-thick crystal. The evolution of dislocation contrast with varying deviation angle Δω revealed a transition from kinematical to dynamical diffraction, in agreement with theoretical predictions based on the dynamical theory. By selectively generating five equivalent two-beam diffraction conditions near the six-beam configuration, the Burgers vectors of individual threading edge dislocations (TEDs) were identified according to the g·b invisibility criterion. The measured line widths of the dislocation images were consistent with calculated values derived from the extinction distance and |g·b| dependence, confirming that most dislocations had a Burgers vector containing a a-type component of *1/3 or *2/3. These results demonstrate that SR-XRT under multi-beam diffraction provides a powerful nondestructive approach for quantitative dislocation analysis in thick GaN crystals, offering valuable insight into defect structures relevant to high-performance GaN-based electronic devices.