Synchrotron radiography and x-ray topography studies of hexagonal habitus SiC bulk crystals

Abstract

Phase-sensitive synchrotron radiation (SR) radiography was combined with x-ray diffraction topography to study structural defects of SiC crystals. The particular bulk SiC crystals examined had a low micropipe density and a hexagonal habitus composed of prismatic, pyramidal, and basal faces well developed. X-ray diffraction topography images of the sliced (0001) wafers, which were formed due to the complex lattice distortions associated with defective boundaries, demonstrated the existence of two-dimensional defective boundaries in the radial direction, normal to the (0001) planes. In particular, those parallel to the 〈1120〉 directions extended rather far from the seed. On the other hand, by phase-sensitive SR radiography the effect of micropipe collection was detected. Micropipes grouped mostly in the vicinities of the defective boundaries but rarely appeared between groups. Some general remarks about possible reasons for the development of such peculiar defect structures were made.

Dislocated micro‐ and nanopipes with surface steps

“…Such a motion realized through the shear step formation has been observed [19,25,26,44] and modelled [25,26,44] using different experimental techniques and theoretical approaches. The lateral pipe motion results from the pipe ramification [25] or occurs due to the pipe interaction with each other, polytype boundaries and other defects.…”

“…This yields:q q 2 ðkÞ ¼ Àð2=pÞ Sðk;ã aÞq q 1 ðkÞ, whereq q 1 ðkÞ is given by (19). After calculation ofq q 2 ðkÞ, the stress field s ð3Þ ij is cast from formula (38) using the Fourier transform method in the same way as the stress field s…”

“…Several authors [16,19] connect the formation of pipes with the presence of low-angle grain (polytype) boundaries at which the pipes are frequently observed [8,19]. Commonly the SiC crystals contain a large number of polytype boundaries which may create strong long-range fields of elastic stresses that influence the dislocation interaction.…”

“…Since the pipes contain superdislocations that create long-range elastic stresses in the crystal, evolution of pipes (their motion [19,20], split [21][22][23][24][25] or coalescence [19,26]) is to a large extent determined by the elastic interaction of their superdislocations with one another, other defects or stressed crystal areas. For example, the split or coalescence of pipes (which may be accompanied by their overgrowth [19,[22][23][24] or the formation of macrovoids [19], respectively) results from the split or coalescence of their superdislocations.…”

“…For example, the split or coalescence of pipes (which may be accompanied by their overgrowth [19,[22][23][24] or the formation of macrovoids [19], respectively) results from the split or coalescence of their superdislocations. Thus, the interaction of pipes with one another and other defects may be of high importance in many different processes.…”