  Principal structural defects in graphene layers, synthesized on a
carbon-terminated face, i.e. the SiC(000) face of a 4H-SiC substrate, are
investigated using microscopic methods. Results of high-resolution transmission
electron microscopy (HRTEM) reveal their atomic arrangement. Mechanism of such
defects creation, directly related to the underlying crystallographic structure
of the SiC substrate, is elucidated. The connection between the 4H-SiC(000)
surface morphology, including the presence of the single atomic steps, the
sequences of atomic steps, and also the macrosteps, and the corresponding
emergence of planar defective structure (discontinuities of carbon layers and
wrinkles) is revealed. It is shown that disappearance of the multistep island
leads to the creation of wrinkles in the graphene layers. The density
functional theory (DFT) calculation results show that the diffusion of both
silicon and carbon atoms is possible on a Si-terminated SiC surface at a high
temperature close to 1600{\deg}C. The creation of buffer layer at the
Si-terminated surface effectively blocks horizontal diffusion, preventing
growth of thick graphene layer at this face. At the carbon terminated SiC
surface, the buffer layer is absent leaving space for effective horizontal
diffusion of both silicon and carbon atoms. DFT results show that excess carbon
atoms converts a topmost carbon layer to sp2 bonded configuration, liberating
Si atoms in barrierless process. The silicon atoms escape through the channels
created at the bending layers defects, while the carbon atoms are incorporated
into the growing graphene layers. These results explain growth of thick
graphene underneath existing graphene cover and also the creation of the
principal defects at the C-terminated SiC(0001) surface
