Electronic\nand Optical Properties of Graphene Quantum\nDots: The Role of Many-Body Effects

Abstract

The\nelectronic structure and optical properties of hexagonal armchair\nand zigzag-edged graphene quantum dots (GQDs) are investigated within\nthe framework of many-body perturbation theory. Many-body effects\nare significant due to quantum confinement and reduced screening.\nThe quasi-particle corrections and exciton binding energies can be\nseveral eV, much larger than those of other carbon allotropes with\nhigher dimensionality. All the GQDs show similar absorption spectra\nwhen electron–hole interaction is included, with a prominent\npeak emerging below the absorption onset of the noninteracting spectrum.\nThis peak is contributed by a pair of double-degenerate excited states\noriginating from the transitions between degenerate frontier orbitals.\nThe spin singlet–triplet splitting is closely related to the\nelectron–hole overlap, which can be approximately measured\nby the overlap between frontier orbitals involved in the optical transitions.\nThe strong many-body effects in GQDs should be of great importance\nin optoelectronic applications.