Effect of electronic structure on carrier multiplication efficiency: Comparative study of PbSe and CdSe nanocrystals

Recently, we demonstrated that PbSe nanocrystal quantum dots can efficiently produce multiple electron-hole pairs (excitons) in response to a single absorbed photon. To address the generality of this carrier-multiplication phenomenon to other materials, we perform a comparative study of multiexciton generation in PbSe and CdSe nanocrystals that have distinctly different electronic structures. We find that both materials exhibit high-efficiency carrier multiplication and the activation threshold is lower in CdSe nanocrystals than in PbSe nanocrystals (similar to 2.5 vs similar to 2.9 energy gaps). Furthermore, the efficiencies of multiexciton generation are nearly identical for both materials despite a vast difference in both energy structures and carrier relaxation behaviors, strongly suggesting that this phenomenon is general to quantum-confined semiconductor nanocrystals. (c) 2005 American Institute of Physics.