In
this work, we identify the nucleation mechanism of threading
dislocations (TDs) associated with stacking faults (SFs) and 15R-SiC
at the early growth stage of 4H-SiC single crystals grown by the
physical vapor transport (PVT) technology. By combining molten KOH
etching and photochemical etching, we successfully reveal etch pits
of TDs and linear etch patterns of SFs on the (112̅0) surface
of 4H-SiC single crystals. Systematic investigations based on transmission
electron microscopy (TEM) observations and Raman analysis indicate
that the Si–C bilayer stacking sequence of SFs is (3, 2) in
Zhdanov’s notation. The accumulation of SFs (3, 2) gives rise
to the polymorph fluctuation and thus the formation of 15R-SiC at
the early PVT growth stage of 4H-SiC single crystals. Quantitative
stress analyses indicate that the strain field distributions along
the SFs (3, 2) and the 15R-/4H-SiC interfaces are inhomogeneous, which
give rise to the nucleation of TDs and low-angle grain boundaries
(LAGBs), respectively. The nucleation of LAGBs releases the high stress
at the 15R-/4H-SiC interface, which facilities the following 4H-SiC
single-crystal growth. Our work indicates that the avoidance of polymorph
fluctuation is important to the reduction of TDs at the early growth
stage of PVT-grown 4H-SiC single crystals.
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