Carrier Multiplication in Nanocrystals via Photostimulated Generation of Biexcitons from Vacuum

TL;DR

This paper introduces a new mechanism for carrier multiplication in semiconductor nanocrystals, where virtual biexcitons are generated from vacuum and converted into real biexcitons via intraband optical transitions, enhancing multiexciton generation efficiency.

Contribution

The study proposes a novel photogeneration mechanism for multiexcitons in nanocrystals involving virtual biexcitons and intraband transitions, which is inactive in bulk materials.

Findings

Mechanism is highly efficient in zero-dimensional nanocrystals.

It can significantly contribute to carrier multiplication in nanocrystals.

Inactive in bulk semiconductors due to momentum conservation.

Abstract

We propose a novel mechanism for photogeneration of multiexcitons by single photons (carrier multiplication) in semiconductor nanocrystals. In this mechanism, the Coulomb interaction between two valence-band electrons involving their transfer to the conduction band creates a virtual biexciton from vacuum that is then converted into a real biexciton by photon absorption on an intraband optical transition. This mechanism is inactive in bulk semiconductors as momentum conservation suppresses intraband absorption. However, it becomes highly efficient in zero-dimensional nanocrystals and can provide a significant contribution to carrier multiplication in these materials.