Through space and through bridge channels of charge transfer at p-n nano-junctions: A DFT study

•Properties of interacting QDs depend on the fashion of interaction: through-bond or through-space.•The disconnected and undoped dimer models shows Fӧrster band formation.•Dimer models with some doping exhibit degenerate charge-transfer excitons.•p- and n-doped qds shows polarization at the interface.•A photoexcitation polarizes p-n interface, in relation to phototovoltaic effect.

Details of charge density distribution at p-n nano interface are analyzed with density functional theory techniques using model system of dimers of doped silicon quantum dots interacting through bond and through space. Spatial distributions of transition densities between the ground and excited states suggest the character of essential electronic excitations, which have a Fӧrster, bound, unbound, or charge transfer character. A redistribution of electronic density from n-impurities to p-impurities results in a ground state polarization and creates an offset of energies of the bands localized on p-doped quantum dot and the bands localized on n-doped quantum dot. Although impurities contribute very few orbitals to the total density, a ground state charge redistribution and polarization are both responsible for the presence of a large number of charge transfer excitations involving solely silicon orbitals.