Carrier multiplication in semiconductor nanocrystals via intraband optical transitions involving virtual biexciton states

Valery I. Rupasov, Victor I Klimov

Research output: Contribution to journalArticle

59 Citations (Scopus)

Abstract

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.

Original languageEnglish
Article number125321
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume76
Issue number12
DOIs
Publication statusPublished - Sep 25 2007

Fingerprint

Optical transitions
optical transition
multiplication
Nanocrystals
nanocrystals
Semiconductor materials
conservation
Conservation
Momentum
Photons
momentum
Impact ionization
Quantum confinement
photons
Valence bands
Coulomb interactions
Conduction bands
conduction bands
Vacuum
valence

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

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abstract = "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.",
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