PNNL

Abstract

Molecular dynamics (MD) methods with a modified Tersoff potential have been used to simulate high-energy (50 keV) displacement cascades in b-SiC. The results show that the lifetime of the thermal spike is on the order of 0.7 ps, 10 times shorter than that in metals, and the surviving defects are dominated by C interstitials and vacancies, which is similar to behavior for 10 keV cascades in SiC. Antisite defects are generated on both sub-lattices. Although the total number of antisite defects remaining at the end of the cascade is smaller than that of Frenkel pairs, the number of Si antisites is larger than the number of Si interstitials. Most surviving defects are single interstitials and vacancies, and only 19% of the interstitial population is contained in clusters. The size of the interstitial clusters is small, and the largest cluster found, among all the cascades considered, contained only 4 interstitial atoms, which is significantly different behavior than obtained by MD simulations in metals. It is observed that all clusters are created by a quenched-in mechanism directly from the collisional phase of the cascade due to the very short lifetime of the thermal spike. The initial Si recoil traveled about 65 nm on average, generating multiple sub-cascades and forming a dispersed arrangement in the cascade geometry. These results suggest that in-cascade or direct-impact amorphization in SiC does not occur with any high degree of probability during the cascade lifetime of Si cascades, even with high-energy recoils, consistent with previous experimental and MD observations.