Silicon carbide (SiC) single crystals have been grown by Physical Vapor Transport (PVT) starting from 15R-SiC seeds. The aim of this work is to study the polytypic transition that usually occurs during the growth of 15R-SiC with a special focus on the interface structure and to analyze the associated mechanism by transmission electron microscopy (TEM). For both Si and C faces, on-axis 15R-SiC seeds have been used. Common growth conditions were employed, i.e. 2200^oC for the growth temperature and a pressure comprised within the 15-20 mbar range.  The thickness of the grown crystals was around 3 mm and the polytype was determined by Raman Spectroscopy. On the C-face, a mixture of 15R-SiC and 4H-SiC was obtained, while on the Si-face, 6H-SiC inclusions were observed. 

Once the transition from 15R-SiC to 4H-SiC or 6H-SiC occurred, it rarely shifted back to 15R-SiC. Defects such as micro-pipes, Stacking Faults (SFs), Basal Plane Dislocations (BPDs), Screw and Edge Dislocation are abundant in 15R-SiC compared to 4H-SiC and 6H-SiC inclusions (Fig.1a). High Resolution Transmission Electron Microscope (HRTEM) was used to examine near atomic sequence at the interface. It revealed micro twin sequence with zigzag (32)/ (23) (Zhdanov notation) pattern in 15R-SiC which may have favored polytypic transformation to 4H-SiC without much disturbing atomic sequence at the interface (Fig.1b) The twin sequences were indistinguishable in Selected Electron Diffraction Pattern (SAED) due to hexagonal polytype inclusion later confirmed by FFT image. The 15R/6H interface was more complex with large transition region due the presence of numerous stacking faults.

Fig1. (a) Convectional TEM image and (b) corresponding  filtered HRTEM shows a coherent transition layer between 15R-SiC and 4H-SiC interface with alternating (32)/ (23) and finally transformed to (32)/(22) atomic sequence. The Zhhdanov notation of the stacking sequence is listed at right was measured as indicated by arrow.

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