a. (001)/(001) crystal
Fig. 3 shows a (001) crystal plate cut from the middle section of the crystal grown on a (001)-oriented seed as shown in Fig. 1(a). Fig. 3(a) and (b) shows the X-ray topographs of the 220 transmission Laue geometry taken from the tail and the peak of the RC, respectively, and panel (c) shows the X-ray topograph of the 400 reflection Bragg geometry taken from the tail of the RC. The interior of the (001) growth sector in the central region exhibits few dislocation defects, no stacking faults and no inclusions, indicating extremely high crystalline quality. It can be confirmed through observation of UV-excited luminescence image that the interior of the (001) growth sector is very pure (Fig. 2(a), [11]). Fig. 3(d) shows the RC of this crystal plate. In the (001) growth sector (the central region) of the crystal grown on a (001)-oriented seed, the RC was almost equivalent to the theoretical value. The small bump on the low-angle side is attributable to the reflection on the rear face. On the other hand, stacking faults are found inside the (111) growth sector. The tail of the entire RC of this crystal (“whole surface” in Fig. 3(d)) is slightly wider because of the effect of the stacking faults inside the {111} growth sectors.