**6. Conclusions**

The evolution of defects was investigated by using on-axis and axial-cut slices prepared from 6*H* and 4*H*-SiC PVT grown crystals. SR phase contrast imaging enabled us to visualize not only MPs and the pores formed at the boundaries of FPIs, but also their changes during SiC growth. Detailed mechanisms for the evolution from FPIs to pores and finally to MPs were suggested. In the early growth stage, FPIs not only induce massive generation of full-core dislocations and MPs but also attract them, forming slit-type pores at the boundaries of FPIs. In the intermediate stage, when FPIs stop to grow and become overgrown by the matrix, the pore density significantly reduces, which is attributed to their transformation into new MPs. In the later stage, the MP density decreases, providing evidence for their partial annihilation and healing.

**References**

*Phys. Lett.*, Vol. 75, 784–786.

*Lett.*, Vol. 83, 2157–2159.

*Phys. Lett.*, Vol. 93, 151905.

497–501.

889–894.

7076–7082.

[1] Argunova, T.; Kohn, V.; Jung, J-W.; Je J-H. (2009). Elliptical micropipes in SiC revealed by computer simulating phase contrast images. *Phys. Status Solidi* A, Vol. 206, 1833–1837.

Characterization of Defects Evolution in Bulk SiC by Synchrotron X-Ray Imaging

http://dx.doi.org/10.5772/52058

43

[2] Baik, S.; Kim, H. S.; Jeong, M. H.; Lee, C. S.; Je, J. H.; Hwu, Y.; Margaritondo, G. (2004). International consortium on phase contrast imaging and radiology beamline at the

[3] Chen, Yi; Dudley, M.; Sanchez, E.; Macmillan, M. (2008). Simulation of grazing-incidence synchrotron white beam X-ray topographic images of micropipes in 4*H*-SiC and

[4] Chernov, A. A. (1989). Formation of crystals in solutions. *Contemp. Phys.*, Vol. 30, 251-276.

[5] Dudley, M.; Huang, X. R.; Huang, W.; Powell, A.; Wang, S.; Neudeck, P.; Skowronski, M. (1999). The mechanism of micropipe nucleation at inclusions in silicon carbide. *Appl.*

[6] Frank, F. C. (1951). Capillary equilibria of dislocated crystals. *Acta Crystallogr.*, Vol. 4,

[7] Gutkin, M. Yu.; Sheinerman, A. G.; Argunova, T. S.; Je, J. H.; Kang, H. S.; Hwu, Y.; Tsai W-L. (2002). Ramification of micropipes in SiC crystals. *J. Appl. Phys.*, Vol. 92,

[8] Gutkin, M. Yu.; Sheinerman, A. G.; Argunova, T. S.; Mokhov, E. N.; Je, J. H.; Hwu Y.; Tsai W-L.; Margaritondo G. (2003). Micropipe evolution in silicon carbide. *Appl. Phys.*

[9] Gutkin, M. Yu.; Sheinerman, A. G.; Argunova, T. S.; Mokhov, E. N.; Je, J. H.; Hwu Y.; Tsai W-L.; Margaritondo G. (2003a). Synchrotron radiographic study and computer simulation of reactions between micropipes in silicon carbide. *J. Appl. Phys.*, Vol. 94,

[10] Gutkin, M. Yu.; Sheinerman, A. G.; Argunova, T. S.; Yi, J.-M.; Kim, M.-U.; Je, J.-H.; Nagalyuk, S. S.; Mokhov, E. N.; Margaritondo, G.; Hwu, Y. (2006). Interaction of micropipes with foreign polytype inclusions in SiC. *J. Appl. Phys.*, Vol. 100, 093518.

[11] Gutkin, M. Yu.; Sheinerman, A. G.; Argunova, T. S.; Yi, J.-M.; Je, J.-H.; Nagalyuk, S. S.; Mokhov, E. N.; Margaritondo, G.; Hwu, Y. (2007). Role of micropipes in the formation of pores at foreign polytype boundaries in SiC crystals. *Phys. Rev.* B, Vol. 76, 064117.

[12] Gutkin, M. Yu.; Sheinerman, A. G.; Smirnov, M. A.; Kohn, V. G.; Argunova, T. S.; Je, J. H.; Jung J.W. (2008). Correlated reduction in micropipe cross sections in SiC growth. *Appl.*

[13] Gutkin, M. Yu.; Sheinerman, A. G.; Smirnov, M. A.; Argunova, T. S.; Je, J.-H.; Nagalyuk, S. S.; Mokhov, E. N. (2009). Micropipe absorption mechanism of pore growth at foreign polytype boundaries in SiC crystals. *J. Appl. Phys.*, Vol. 106, 123515.

determination of their dislocation senses. *J. Electron. Mater.*, Vol. 37, 713–720.

Pohang Light Source. *Rev. Sci. Instrum.*, Vol. 75, 4355–4358.

The reactions of MPs in view of their elimination during the crystal growth were briefly reviewed. The reduction of MP cross-section, which can eventually results in its overgrowth, occurs at the crystal growth when MP splits, as well as merges or interacts with another MP in a non-contact mode. The split happens if the splitting dislocation overcomes the MP attraction zone and the flat crystal surface attraction zone. Merging can occur due to collective mesoscopic effects in a random ensemble of MPs. The twisted dipoles result under the action of neighboring MPs. When the magnitudes of Burgers vectors are the same, the dipole is transformed into a new configuration of a semiloop. Such reactions of ramification and coalescence of MPs, as well as annihilation for dipoles of MPs, were observed by phase-contrast imaging. Computer simulation of phase-contrast images demonstrated the correlated reduction in the radii of two remote MPs, which provided a support of contact-free reaction between them.

This study suggests that the key point for the elimination of defects from such crystals is the suppression of FPI nucleation. The reactions of MPs are necessary for diminishing their density; and such reactions should be faster as the surface energy becomes smaller.

### **Acknowledgements**

This work was supported by the Creative Research Initiatives (Functional X-ray Imaging) of MEST/KOSEF of Korea. The work of VGK was supported by RFBR grant No. 1002-00047-a.
