Numerical study of carrier multiplication pathways in photoexcited nanocrystal and bulk forms of PbSe.

Employing the interband exciton scattering model, we perform a numerical study of the direct photogeneration and population relaxation processes contributing to carrier multiplication (CM) in nanocrystalline and bulk PbSe. We argue that in both cases the impact ionization is the main mechanism of CM. This explains the weak contribution of the direct photogeneration to the total quantum efficiency (QE). An investigation of the size scaling of QE in nanocrystals and a comparison to the bulk limit provide microscopic insight into the experimentally observed trends.