Structural disordering and extended defects produced by He-implantation in silicon carbide

Microstructure in He implanted 4H-SiC under severe conditions followed by high-temperature annealing was studied by high-resolution transmission electron microscopy (HRTEM) using a Cs-corrected microscope. A huge density of stacking faults between large cavities was observed in the highly damaged zone. In order to get quantitative insights into the mechanisms operating in the stacking formation, HRTEM experiments and image simulations were completed by atomic structure calculations. Complex defects involving both Frank dislocations (FDs) and Shockley partial dislocations (PDs), which can either constitute scattering or compact fronts of dislocations, were revealed by HRTEM. In the latter case, the core of these complex defects extends over a few adjacent glide-set planes and the collective propagation of the PDs is associated with the formation of disordered ‘nanobands’ in the initial SiC microstructure. Multislice simulations of the experimental contrast of the FDs showed that they are formed by the condensation of a Si-C bi-layer. The gliding of the PDs allows accommodating the bending of the structure induced by the growth of FDs and is thermodynamically activated by polytypic transformation induced by the multiple shearing of basal planes, as calculated by using the axial next-nearest-neighbour Ising model.