【World Express】Nondestructive Testing of Lattice Defects in β-Gallium Oxide Crystals

Using X-ray abnormal transmission phenomenon，internal defects can also be detected and classified in thick crystals

  In December 2022, JFCC in Japan announced its cooperation with NCT and Hyogo University to successfully detected and observed all the crystal defects in β-Ga₂O₃ crystal with thickness about 0.7mm  in a non-destructive manner in a short time, using the X-ray abnormal transmission phenomenon. For next generation power semiconductors, high quality β-Ga₂O₃ crystal is expected to be improved.

  Methods such as "X-ray topography observation" have been used for evaluation defect distribution in  β-Ga₂O₃ crystal. However, due to the existence of Ga, defects from the surface to the depth of 0.02 mm can only be observed using conventional methods.

  In this study, the X-ray topography observation method of abnormal transmission phenomenon was used to obtain the spatial distribution information of defects in the crystal and the information that can identify the types of defects. Abnormal transmission refers to the sharp reduction of X-ray absorption in the presence of standing waves at the junction with the atomic surface. This phenomenon leads to a significant increase in the intensity of the transmitted X-ray.

10 x 15 mm (001) flat, X-ray Abnormal transmission  topography of β-Ga₂O₃ single crystal substrate

来源：JFCC等

Position relationship between standing wave and atomic surface generated by interference between incident wave and diffraction wave

来源：JFCC等

  The lattice defect area inside the crystal will not produce abnormal transmission, and the intensity of the transmission wave will decrease regionally. Therefore, if abnormal transmission occurs in the whole crystal and the intensity distribution of the transmission wave is observed, it is possible to confirm that there are lattice defects in the X-ray weak region.

Schematic diagram of optical system of  abnormal transmission X-ray topography observation method

  In the experiment, to determine whether abnormal transmission occurred, the intensity of transmission wave and diffraction wave on the fluorescent plate were observed. Under the condition of strong normal X-ray absorption (no abnormal transmission), the transmission wave is very weak. Under the condition of abnormal transmission, two extremely strong transmission and diffraction wave points appear. If the fluorescent plate is removed in this state and the intensity distribution of the transmitted wave is taken with a camera, the defect distribution in the X-ray irradiation area can be determined.

Fig. a) shows the intensity of transmitted and diffracted waves observed on the fluorescent plate, to determine whether abnormal transmission occurs.

Fig. b)  is taken under the condition of non abnormal transmission.

Fig. c) shows two extremely strong transmission and diffraction wave points.

  In this experiment, the types of defects can be identified. In X-ray topography observation, the contrast of defects depends on the relative relationship between diffraction conditions and lattice defect types. Therefore, if the defects at the same position are compared and analyzed under several diffraction conditions, the type of defects can be determined.

X-ray topographic map at the same position under several diffraction conditions