Multi-carrier processes in halogenated Si nanocrystals

We study theoretically an effect of passivation with Cl and Br on Auger recombination and multiple exciton generation in silicon nanocrystal Si₃₁₇X₁₇₂, with X being the passivating element. The nanocrystal electronic structure and rates of these processes are calculated using time-dependent density functional theory. Comparison with the H-passivated Si nanocrystal shows that the bromine coating, despite having less electronegativity, affects the electronic structure and transition rates more than the chlorine one due to the stronger structural perturbations caused by the greater surface atoms. Certain electron-hole asymmetry in both of the considered multi-carrier processes is revealed for the Br-coated silicon nanocrystal: the processes become faster if initiated by holes and slower (or invariable on the whole) if initiated by electrons. On the contrary, the chlorine coating weakly influences the multi-carrier processes.