Effects of nanoindentation tip radius on the first dislocation pop-in behavior in 4H SiC single crystal

The nano-scaled defect generations and mechanics for the hexagonal 4H SiC semiconducting single crystals are examined systematically by using nanoindentation tests on the {0001} basal plane. The dislocation defects induced by outside accidental applied load or internal residual stress by thermal cycling during fabrication or prolonged usage would impose a significant influence on the semiconductor performance. To more closely examine the indent tip stress concentration effects, we adopted three tips with different tip radii of curvatures R, the blunt, medium, and sharp tips with R∼150, 50, and 20 nm. The stress for the first dislocation pop-in was measured to be 16.1, 14.8, and 13.2 GPa, demonstrating the stress concentration effect beneath the indent tip. With a sharper tip, the stress for the first dislocation pop-in would be lower. The first pop-in displacement under the blunt or sharp indent tip was measured to be about 10 or 1 nm, likely a result of the threading screw dislocation along the vertical [0001] sliding downward by about 10 or 1 Burgers vector. The stress for the first activation of moving dislocation in the 4H SiC crystal is close to the final saturated flow stress. There is minimum work hardening.