We propose and analyze a physical mechanism for photogeneration of multiexcitons by single photons (carrier multiplication) in semiconductor nanocrystals, which involves intraband optical transitions within the manifold of biexciton states. In this mechanism, a virtual biexciton is generated from nanocrystal vacuum by the Coulomb interaction between two valence-band electrons, which results in their transfer to the conduction band. The virtual biexciton is then converted into a real, energy-conserving biexciton by photon absorption on an intraband optical transition. The proposed mechanism is inactive in bulk semiconductors as momentum conservation suppresses intraband transitions. However, it becomes highly efficient in the case of zero-dimensional nanocrystals, where quantum confinement results in relaxation of momentum conservation, which is accompanied by the development of strong intraband absorption. Our calculations show that the efficiency of the carrier multiplication channel mediated by intraband optical transitions can be comparable to or even greater than that for impact-ionization-like processes mediated by interband transitions.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Sep 25 2007|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics