Structural, electronic and optical properties of SiC quantum dots

We perform density functional theory calculations of the hydrogen-passivated topological silicon carbide quantum dots (QDs) and investigate their structural, electronic and optical properties. We study clusters constructed from 3C-SiC with up to 8 topological shells, corresponding to diameters up to 2.2 nm, terminated homogeneously with either Si-H or C-H bonds. All QDs exhibit tensile strain (1-5 %) within the cluster core. The larger the cluster, the smaller the strain in the interior, however. Tensile strain increases from the inside of the cluster towards the outside, reaches a maximum at the second layer below the surface, and vanishes only for bonds involving surface Si or C atoms. Quantum-confinement effects are observed for the energy gaps and optical gaps of SiC QDs. Size has a major impact on the absorption edge in comparison to a weak effect on the photon energy of the spectra maxima. Our calculations show that surface termination plays a crucial role and strongly affects energy gaps, optical gaps and optical spectra. Orbitals around the HOMO-LUMO gap predominantly localize within the core of the cluster, with significant contributions by the surface for Si-H terminated clusters only.