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Semiconductor excitons in new light

Nature Materials volume 5, pages 523–531 (2006)Cite this article

Abstract

Excitons are quasi-particles that form when Coulomb-interacting electrons and holes in semiconductors are bound into pair states. They have many features analogous to those of atomic hydrogen. Because of this, researchers are interested in exploring excitonic phenomena, from optical, quantum-optical and thermodynamic transitions to the possible condensation of excitons into a quantum-degenerate state. Excitonic signatures commonly appear in the optical absorption and emission of direct-gap semiconductor systems. However, the precise properties of incoherent exciton populations in such systems are difficult to determine and are the subject of intense debate. We review recent contributions to this discussion, and argue that to obtain detailed information about exciton populations, conventional experimental techniques should be supplemented by direct quasi-particle spectroscopy using the relatively newly available terahertz light sources. Finally, we propose a scheme of quantum-optical excitation to generate quantum-degenerate exciton states directly.

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Figure 1: Excitonic absorption spectra for a GaAs-type quantum-well system.
Figure 2: Resonant excitation dynamics.
Figure 3: The influence of exciton populations on ‘excitonic’ photoluminescence spectra in quantum wells.
Figure 4: Excitonic THz absorption spectra.
Figure 5: Quantum degenerate exciton distribution generated by resonant excitation with incoherent light.

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Acknowledgements

The research in Marburg is partially supported by the Deutsche Forschungsgemeinschaft through the Quantum Optics in Semiconductors Research Group and the Optodynamics Centre at the Philipps-Universität Marburg. We thank W. Hoyer for valuable discussions and collaboration on the exciton-luminescence theory. The Tucson research is financed by NSF (AMOP), AFOSR and DURINT.

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  1. Department of Physics and Material Sciences Centre, Philipps-Universität, Renthof 5, D-35032, Marburg, Germany

    S. W. Koch & M. Kira

  2. College of Optical Sciences, University of Arizona, Tucson, Arizona, 85721, USA

    G. Khitrova & H. M. Gibbs

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Correspondence to S. W. Koch.

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Koch, S., Kira, M., Khitrova, G. et al. Semiconductor excitons in new light. Nature Mater 5, 523–531 (2006). https://doi.org/10.1038/nmat1658

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