First principles analysis of impurities in silicon carbide grain boundaries

Silicon carbide is an important structural and electronic ceramic material that finds many uses in a wide variety of applications that require stability at extreme conditions. In this study, we provide a detailed investigation of the formation energies of point defects and the stability of a wide variety of dopants in bulk cubic silicon carbide (3C-SiC) and in 3C-SiC grain boundaries (GBs) using first principles methods and a detailed charge distribution analysis. We also determine the driving force (segregation energies) of these dopants towards GBs. Our results show that smaller, more electronegative elements such as oxygen and nitrogen occupy carbon substitutional sites whereas larger transition metals such as molybdenum and rare earth elements such as cesium, substitute for silicon sites in SiC. Such dopants tend to migrate to more open spaces as provided in the Σ9 GB. This suggests that Σ9 GB is more effective in pinning the defect centers as compared to Σ3 GB. These findings provide the chemical landscape for defect engineering through which doped 3C-SiC can be designed for targeted materials development purposes.