Giant excitonic exchange splitting in Si nanowires: First-principles calculations

The size and doping dependence of the electron-hole exchange interaction in Si nanowires is investigated from first principles. In pure Si nanowires we found excitonic exchange splittings in very good agreement with the experimental results for porous silicon. For n-doped Si nanowires a giant singlet-triplet splitting, three order of magnitude bigger than in bulk silicon, is predicted as due to the dramatic enhancement of the electron and the hole probability of being in the same place at the same time.