Role of micropipes in the formation of pores at foreign polytype boundaries in SiC crystals

Abstract

The role of micropipes in pore formation in SiC crystals with foreign polytype inclusions is studied by means of synchrotron phase sensitive radiography, optical and scanning electron microscopies, and color photoluminescence. The pores at the inclusion boundaries are revealed, and their shapes and locations are analyzed. It is found that the pores arise due to the attraction of micropipes by the foreign polytype interfaces, followed by micropipe coalescence. The observed pores have tubular or slit shapes. Tubular pores nucleate at the inclusion corners, where the inclusion-associated stresses are concentrated. Slit pores spread between them and follow the shape of the inclusion boundaries. We explain the observations within a two-dimensional model of elastic interaction between micropipes and inclusion boundaries, which accounts for free surfaces of micropipes.

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

“…3(a) demonstrates that the groups of pores (marked by black and white arrows) consist of short tube-shaped or slit-like segments. The morphology of such pores was investigated and attributed to the elastic interaction between MPs and boundaries of FPIs, resulting in coalescence of MPs into larger pores elongated along the boundaries [11,13]. FPIs were indeed observed on the same location, as revealed by the yellow PL images [28] of n-type 4H-SiC containing N and B in Fig.…”

“…The attraction of the MPs to the pore was suggested and explained by their absorption to pores [11,13]. We believe that, at the initial stage of growth, the pores are generated by the attraction of MPs by FPIs, followed by MP coalescence [10,11].…”

“…If generated, then the stages described above are repeated. However, though formed as explained in the intermediate stage, MPs can be attracted to FPIs and absorbed by their boundaries, producing extended pores there by agglomeration [10,11]. If new FPIs are not nucleated, the processes of self-organization occur in the MPs ensemble: MPs elastically interact and react with each other as well as with full-core dislocations, as described in the section 4.…”

“…High densities of interface dislocations and vacancies thus formed possibly lead to coagulation of vacancies, forming slit-like pores along the FPI boundaries. Another possible mechanism of pore formation is the attraction and agglomeration of MPs at FPI boundaries [10,11,13], for instance, resulting in the majority of pores observed at the boundaries of FPIs (Fig. 3).…”

“…The nucleation of FPIs in the initial stage is suggested as a basis of massive generation of full-core dislocations [26], pores and MPs [10,11,13,31]. The bottom and lateral faces of growing FPIs are possibly the formation sites of interface dislocation structures to accommodate the misfit or misorientation of the matrix and FPI's crystalline lattices.…”