Structural Characterization of Dot-Core GaN Substrates with Annealing Under Growth-Like Conditions Using Synchrotron Monochromatic X-ray Topography

In this work, synchrotron monochromatic X-ray topography was employed to study the structural characteristics of as-received c-plane dot-core GaN substrates and then to investigate the structural evolution with annealing under growth-like conditions at 1050 °C for 10 h. Single exposure X-ray topography images were obtained using the (11 2 4) GaN asymmetric reflection. These images were superimposed to quantify the lattice distortions in regions near the dot-cores and in the regions between these defects. The results show that different dot-core substrates from the same vendor exhibit different defect distribution, lattice distortions around the cores, and different radii of lattice curvature, ranging from 7 m to 25 m. Annealing under growth-like conditions reduces both the global and local lattice distortions. Globally, the radius of curvature across the wafer increased from 17 m to 27 m after annealing. The local radius of curvature across the highly distorted core regions also increased from 0.47 ± 0.04 m to 0.9 ± 0.2 m after annealing. An increase in the radius of curvature is an indication of stress reduction. The lattice tilt around the cores varies from 0.01°−0.02°. The lattice planes around the centers of cores are highly distorted, and the magnitude of the tilt generally decreases radially away from the core center. After annealing, these local distortions decreased as well. A general core model was built based on these experimental results, providing a fundamental structural picture of dot-core regions, which has been lacking in the current literature.