Ge cages at the SiC/graphene interface: A first principles calculation

Using the first principles density functional theory calculations, we investigated the effect of Ge atoms on the electronic and structural properties of epitaxial graphene on the Si-face of SiC. We considered both the substituted Ge atoms and intercalated multilayers of Ge at the interface. Starting with Ge3 clusters, we introduce one to six monolayers (ML) of Ge at the interface. Our first-principles density functional theory (DFT) calculations find that, when there are more than four ML, the periodicity of the most stable atomistic configuration of Ge atoms in between the buffer layer and the SiC substrate is influenced by the periodicity of the substrate underneath, as well as the periodicity of the honeycomb array of C atoms on the top. Two distinct Ge cages are formed which are merged in to each other. As a result of the intercalation, the buffer layer decouples from the substrate converting it to graphene. Within the scope of our calculations, we found electron-doped graphene with Ge intercalation.