Ab initio study of interstitial helium clusters in 3C-SiC

Abstract

Ab initio calculations were carried out to investigate the behaviors of interstitial Hen clusters in 3C-SiC. Based on the simulation and experimental results of SiC, we considered two types of tetrahedral sites for He atoms to be allocated, forming an interstitial Hen cluster. The compact structures of Hen clusters that were alternately surrounded by the tetrahedral sites neighboring four Si atoms (TSi) and the tetrahedral sites neighboring four C atoms (TC) were investigated, and the corresponding number of tetrahedral sites in each TSi or TC layer was determined by an empirical formula. To better illustrate the interaction between He atoms, we defined one and two types of ground states when calculating the binding energies at high and low temperatures, respectively. The average binding energies of each He atom in Hen clusters of different sizes were obtained, and the maximum binding energy of a He atom in the outermost layer of a Hen cluster was estimated to be 0.61 eV via the number of nearest neighboring and next nearest neighboring He atoms. It is of interest to note that the self-trapping mechanism was not observed in 3C-SiC, since He atoms remained in their respective tetrahedral sites at low temperatures due to their high migration barrier and weak binding energy. In contrast, the compact Hen clusters tended to dissolve at high temperatures because the He atoms located at TC sites tended to migrate into TSi sites.