Defect accumulation in 4H-SiC due to light ion irradiation near nuclear elastic scattering resonances.

Single-crystal silicon carbide (4H-SiC) was irradiated with 1570 keV hydrogen (H) ions and 4200 keV helium (He) ions in order to investigate the nature of the damage that might be induced by exposure to protons, fast neutrons, or alpha particles in a nuclear reactor or waste storage environment. Raman spectroscopy and ion beam channeling were used to investigate the extent and nature of the disorder caused by light ion irradiation just under the surface of the material, rather than at the end of the ion beam range. The results suggests that the Monte Carlo simulation program SRIM correctly predicts the relative amount of ballistic displacement induced by H and He ions, as measured by the number of antisite defects and extinction of characteristic Raman features, with complete chemical disorder achieved at less than 0.10 displacements per atom (dpa). In contrast, ion beam channeling measurements indicated that full structural disorder (amorphization) required much higher levels of atomic displacement. In the case of H irradiation, the rate of disorder accumulation was consistent with the direct-impact / defect-stimulated (DI/DS) model found in other studies, with no evidence of temperature-induced defect recombination. In the case of He irradiation the overall amount of amorphization and loss of crystallinity was only 25% of that expected from the same low-temperature DI/DS model. These results are discussed in light of a possible ionization-induced recrystallization or defect recombination mechanism induced not directly by the He ion, but by ionization in the cascades of the highest energy recoil atoms.