Etch pit formation on β-Ga2O3 by molten KOH+NaOH and hot H3PO4 and their correlation with dislocations

We performed Borrmann effect x-ray topography (XRT) to observe dislocations and other structural defects in a thick β-Ga2O3 (001) substrate. The Borrmann effect was realized by working in a symmetrical Laue geometry ( g = 020). 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 analysis clearly revealed straight b-axis screw-type and curved dislocations and allowed assessing the corresponding behaviors. Other structural defects, including pipe-shaped voids and dislocation loops produced by mechanical damage, were also observed. Finally, we compared Borrmann effect transmission topography and conventional reflection topography and explained the appearance of some characteristic defects in the two modes. 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-Ga2O3.

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Observation of dislocations in thick β-Ga2O3 single-crystal substrates using Borrmann effect synchrotron x-ray topography

Yao

Hirano

Sugawara

et al. 2022

APL Materials

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Large-area total-thickness imaging and Burgers vector analysis of dislocations in β -Ga2O3 using bright-field x-ray topography based on anomalous transmission

Yao

Tsusaka

Kuramata³

et al. 2022

Applied Physics Letters

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Using bright-field x-ray topography based on anomalous transmission (AT), we have demonstrated the first large-area total-thickness imaging of dislocations in β-Ga2O3 at the substrate scale. The dislocation images were acquired from the entire 10 mm × 15 mm × 680 μm (001)-oriented substrate prepared by edge-defined film-fed growth (EFG) by stitching together hundreds of topographic images, each recorded with the forward-diffracted beam in the Laue geometry for g = 020, 0–20, 022, and 400, under the conditions in which AT occurred. Dislocations distributed over the entire crystal volume were imaged as long as their Burgers vectors ( b) were not orthogonal to the g-vectors. The results of the g· b analysis of the dislocation contrasts clearly revealed three major dislocation types that were numerically dominant in the EFG crystal: (i) b-axis screw-type dislocations with b∥ ξ∥[010] ( ξ is the unit vector of line direction), (ii) b-axis edge-type dislocations with b∥[001] and ξ∥[010], and (iii) curved mixed-type dislocations lying on the (001) planes with b∥[010]. Based on their b - and ξ-vectors, types (i) and (ii) were attributed to dislocations that propagated during EFG pulling up along the [010] direction, while type (iii) was attributed to dislocations generated through glide in the [010](001) slip system under stress. The extent to which AT can manifest itself is explained by using the effective absorption coefficient calculated for the above g-vectors based on dynamical x-ray diffraction theory.

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Three-dimensional distribution and propagation of dislocations in β-Ga2O3 revealed by Borrmann effect x-ray topography

Yao,

Tsusaka,

Hirano

et al. 2023

Journal of Applied Physics

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Synchrotron radiation x-ray topography (XRT) in a transmission configuration based on the Borrmann effect (BE) was carried out to observe characteristic dislocation structures and three-dimensional distribution and propagation of dislocations in β-Ga2O3 grown via the edge-defined film-fed growth (EFG) method. Substrates with a range of surface orientations of (001), (010), and (2¯01), cut perpendicular or parallel to the ⟨010⟩ growth direction of the EFG, were observed to understand the whole picture of dislocations distributed in the bulk crystals. Using the (001)-oriented substrate, we found characteristic dislocation structures such as dislocation helices, damage-related (001)-plane dislocation networks, and tangled dislocation complexes, which exist universally in EFG crystals but have rarely been reported before. A careful measurement of the dislocation length in BE-XRT images taken with different g-vectors allows us to determine the crystal plane on which a dislocation lies. The BE-XRTs taken from the (010)-oriented and (2¯01)-oriented substrates suggested that the dislocations propagating along the [010] growth direction were dominant. Most of these b-axis threading dislocations had a Burgers vector of [010] or [001], and they tended to align in the (100) plane. The BE-XRT observations in this study provide valuable knowledge for understanding the structure and character of dislocations in β-Ga2O3.

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Etch pit formation on β-Ga2O3 by molten KOH+NaOH and hot H3PO4 and their correlation with dislocations

Cited by 7 publications

References 33 publications

Observation of dislocations in thick β-Ga2O3 single-crystal substrates using Borrmann effect synchrotron x-ray topography

Observation of dislocations in thick β-Ga2O3 single-crystal substrates using Borrmann effect synchrotron x-ray topography

Large-area total-thickness imaging and Burgers vector analysis of dislocations in β -Ga2O3 using bright-field x-ray topography based on anomalous transmission

Three-dimensional distribution and propagation of dislocations in β-Ga2O3 revealed by Borrmann effect x-ray topography

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