Basal plane dislocations (BPDs) are one of the most harmful dislocations in 4H silicon carbide (4H-SiC). Understanding the nucleation of BPDs is the basis of reducing the density of BPDs in 4H-SiC. In this work, we investigate the nucleation mechanism of BPDs, as well as the effect of doping on the nucleation of BPDs in 4H-SiC using nanoindentation. It is found that the shear stress plays a dominant role in the nucleation of BPDs in undoped 4H-SiC. This indicates that the thermal stress during the growth of 4H-SiC single crystals and mechanical stress during the processing of 4H-SiC wafers both give rise to the nucleation of BPDs. Nitrogen (N) doping is found to facilitate the BPD nucleation and decreases the shear stress required for the formation of BPDs. In contrast, vanadium (V) doping hinders the nucleation of BPDs, which promotes the polymorph transition from 4H-SiC to 3C-SiC.

In this work, the anisotropic deformation and anisotropic mechanical properties of 4H silicon carbide (4H-SiC) single crystal wafers are proposed using nanoindentation. The C face of 4H-SiC wafer shows higher hardness and lower fracture toughness than those of the Si face. Because the deformation of 4H-SiC is assisted by the nucleation and slip of basal plane dislocations (BPDs), especially the slip of the Si-core partial dislocation (PD) of the BPDs, the nucleation and slip of the Si-core PD in the Si face of 4H-SiC is easier than those in the C face, which releases the nanoindentation-induced stress and results in the decrease of the hardness and increase of the fracture toughness of the Si face of 4H-SiC wafers. Due to the hexagonal lattice of 4H-SiC, the hardness along the 〈11 ̅00〉 direction of 4H-SiC is higher than that along the 〈112 ̅0〉 direction, but the fracture toughness along the 〈11 ̅00〉 direction is lower than that along the 〈112 ̅0〉 direction, as a result of the enhanced glide of dislocations along the most closely packed direction. The insights gained in this work are expected to shed light on the optimization of the mechanical processing of 4H-SiC wafers.