Multi-analytical study of syntactic coalescence of polytypes in a 6H-SiC sample

X-ray diffraction topography (XRDT), using both synchrotron white-beam (SWBXT) and conventional MoKα1 radiation, μ-Raman spectroscopy and transmission electron microscopy (TEM) were used to study a complex syntactic coalescence of polytypes in a PVT-grown 6H-SiC sample. The combined use of these techniques has proven to be well suited to determine twin-related lamellae of polytype 15R. Each single technique used here was not fully adequate to establish the polytypic nature and the geometric relationship between the lamellae of foreign polytypes and the surrounding crystal bulk. X-ray diffraction topographies showing the whole slice, enabled the location of three lamellae: one lamella, labelled L1, and two micro-lamellae L2 and L3. Lamella L3 was enclosed in L1. The diffraction contrast analyses and the μ-Raman spectra indicated that the L1 and L2 lamellae were exactly iso-oriented and both consisted of the 15R polytype, whereas the polytype of the L3 lamella could not be clearly determined. Transmission electron microscopy (TEM) enabled a more thorough investigation of the actual polytype of this lamella. TEM analyses were carried out on a small fragment embedding the L3 lamella and these indicated that L3 was a 15R polytype which was twin-related by a rotation of 180° about the [0 0 0 1] axis with a (0 0 0 1) compositional plane.