Lattice damage and nanohardness in 6H-SiC implanted with multiple-energy Xe ions

Specimens of 6H-SiC were implanted with Xe ions with multiple kinetic energies at room temperature to obtain nearly uniform Xe concentrations of 7.5, 30, 150 at. ppm, respectively, and were subsequently thermally annealed under high vacuum. The lattice damage and nanohardness of specimens were studied with high resolution X-ray diffraction spectrometry and nanoindentation measurements. In the low dose specimen (7.5 at. ppm), the occurrence of a plateau (with sub-peaks) at low angle side of the SiC (0 0 0 1 2) peak suggests a strain gradient in the direction normal to the specimen surface. Upon subsequent thermal annealing the strain relaxes gradually. The relaxation activation energy of the strain was estimated with Arrhenius law. For the specimens implanted to 30 and 150 at. ppm Xe, the disappearance of the plateau or peak indicates that the implanted region has been amorphized. However, a satellite peak near the main peak reappears after the thermal annealing. In addition, the main peak broadens toward high angle side after the annealing as the result of a shrinkage of crystal lattice. The nanohardness value of the specimen implanted to 7.5 at. ppm exceeds that of virgin SiC, whereas it is opposite for the case of 30 and 150 at. ppm implantation due to the formation of amorphous regions. Changes of nanohardness with thermal annealing temperature were studied. Underlying mechanisms were discussed.