Search

We investigate the crack-healing mechanism of 4H silicon carbide (4H-SiC) and reveal the effect of dopants on the crack-healing behavior of 4H-SiC. Vickers indentation tests and thermal annealing are utilized to generate cracks and heal cracks in 4H-SiC, respectively. High-temperature thermal annealing in the air atmosphere is found to be capable of effectively healing indentation-induced cracks and releasing indentation-induced stress in undoped 4H-SiC by the formation and viscous flow of glass phase SiO2. Nitrogen (N) doping is found to assist the atomic diffusion of 4H-SiC. The crack healing of N-doped 4H-SiC is realized by the synergy of host solid diffusion and the padding of glassy SiO2. In contrast, vanadium (V) doping hinders the viscous flow of SiO2 and results in the incomplete healing of cracks in V-doped 4H-SiC. Although the generation of cracks lowers the bending strength of 4H-SiC, the healing of cracks by the padding of glassy SiO2 is found to effectively recover the bending strength of indented 4H-SiC samples. Our work opens a pathway to design thermal processing technologies to heal the cracks and enhance the mechanical properties of 4H-SiC wafers. [ABSTRACT FROM AUTHOR]

A 4H-SiC single crystal is a substrate material for high-frequency and high-voltage power devices. Dislocation density is a fundamental criterion for evaluating the quality of 4H-SiC single crystals. 4H-SiC single crystals grown by the physical vapor transport (PVT) method generally have high dislocation density. To investigate the effect of nitrogen doping on dislocation proliferation in SiC crystals, the thermal field of the ingot during PVT growth was calculated by COMSOL Multiphysics, and thermal stress was calculated by thermal elastic theory. Finally, the dislocation density of the crystal was calculated based on the Alexander–Haasen model for inhomogeneous nitrogen doping. By comparing the calculation and experimental results, we proposed a possible value of the effective stress to evaluate the effect of a nitrogen dopant on dislocation density, which helps calculate the dislocation density in the n-type SiC. [ABSTRACT FROM AUTHOR]

The role of dopants on deformation and mechanical properties of 4H silicon carbide (4H-SiC) is proposed by using nanoindentation. It is found that the hardness, elastic modulus, and fracture toughness of 4H-SiC substrate wafers all decrease on the order of vanadium (V) doping, undoping, and nitrogen (N) doping. For all three types of 4H-SiC, basal plane dislocations (BPDs), threading edge dislocations, and cracks are formed during the nanoindentation. Polymorph transitions from 4H-SiC to amorphous SiC and 3C-SiC are found as the penetration depth of the indent increases from the subsurface to the deeper region. N doping is found to weaken the bond strength of 4H-SiC, which enhances the glide and piling up of BPDs in nanoindentated N-doped 4H-SiC. In contrast, V doping effectively hinders the glide of BPDs, which accumulates a high-stress field and facilitates the polymorph transition from 4H-SiC to 3C-SiC and amorphous SiC. The insight on the effects of dopants on the deformation and mechanical properties of 4H-SiC may help the design of the processing of differently doped 4H-SiC substrate wafers. [ABSTRACT FROM AUTHOR]