To perform transmission topography measurements, one way to circumvent the thickness requirement is to take advantage of the anomalous transmission of x rays, a dynamical diffraction phenomenon also known as the Borrmann effect. 20,21 Because transmission topographs are not available, the three-dimensional (3D) distribution of dislocations in the interior of β-Ga 2O 3 remains unknown this precludes the analysis of the behavior of dislocations on a wafer scale, such as their generation, multiplication, and interaction during crystal growth. 19 It is extremely difficult to obtain such thin crystals because of the high cleavability and high brittleness of β-Ga 2O 3. Obtaining transmission topography images of β-Ga 2O 3 based on extinction contrast would require a very thin crystal (<100 µm) to satisfy the μt ∼ 1 condition (where μ is the linear absorption coefficient and t is the sample thickness). This is mainly due to the high x-ray absorption of β-Ga 2O 3 because of the presence of heavy Ga atoms. To the best of our knowledge, no successful transmission topography (Laue case) observations have been reported for this material. 11–18 In this configuration, the penetration depth of the x rays is typically no greater than 20 μm 15 therefore, dislocations in the deeper regions of the crystals cannot be imaged. However, XRT observations of β-Ga 2O 3 have been limited to reflection topography measurements based on the Berg–Barrett configuration (Bragg case). Our results show that Borrmann effect XRT is a powerful and effective technique to study the spatial distribution and structural properties of defects in highly absorbing β-Ga 2O 3. Finally, we compared Borrmann effect transmission topography and conventional reflection topography and explained the appearance of some characteristic defects in the two modes. Other structural defects, including pipe-shaped voids and dislocation loops produced by mechanical damage, were also observed. The analysis clearly revealed straight b-axis screw-type and curved dislocations and allowed assessing the corresponding behaviors. Anomalous transmission occurred under the exact Bragg condition, producing a strong diffraction beam that allowed us to image defects across the entire thickness of the substrate. The Borrmann effect was realized by working in a symmetrical Laue geometry ( g = 020). We performed Borrmann effect x-ray topography (XRT) to observe dislocations and other structural defects in a thick β-Ga 2O 3 (001) substrate.
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