Near-atomic images of interfaces between twin-related lamellae in a synthetic 6H-SiC sample

Transmission Electron Microscopy (TEM) and High Resolution TEM (HRTEM) investigations were used to study a complex micro-structure of twin-related lamellae of 15R SiC polytype, in syntactic coalescence with 6H-SiC. The analysis of the local stacking microstructure by means of HRTEM revealed that the perfect structure of 15R polytype, (23)3 was locally interrupted by numerous adjoining stacking faults parallel to (0001) with stacking of the coupled (22) and (33) bilayers superimposed on the twin boundaries. HR images taken exactly across both the twin boundaries showed a zig-zag pattern (23) that switched to (32) by a twin coherent interfaces or, alternatively, a zig-zag pattern (32) which passed to (23) through an isolated (33), 6H like sequence. The selected area electron diffraction (SAED) patterns taken exactly above both the twin interfaces indicate classifying of the twin found in this study as a "Friedelian" reticular merohedric twinning. However, two indistinguishable twin operations matched the observed features: a reflection through rational plane (0001), and 180°-rotation around [0001]. Since individual Si and C atoms and even the SiC bilayer polarity could not be established from these HR images, the real twin law was deduced by taking into account that the coherent structural match at the interface could be guaranteed only by a 180°-rotation around [0001]. In order to explain the origin of the planar defects found in this sample, the growth mechanism and the influence of the low-energy stacking faults were considered. © 2010 Springer-Verlag.