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Long lifetimes of quantum-dot intersublevel transitions in the terahertz range

Nature Materials volume 8, pages 803–807 (2009)Cite this article

Abstract

Carrier relaxation is a key issue in determining the efficiency of semiconductor optoelectronic device operation. Devices incorporating semiconductor quantum dots have the potential to overcome many of the limitations of quantum-well-based devices because of the predicted long quantum-dot excited-state lifetimes. For example, the population inversion required for terahertz laser operation in quantum-well-based devices (quantum-cascade lasers1,2) is fundamentally limited by efficient scattering between the laser levels, which form a continuum in the plane of the quantum well. In this context, semiconductor quantum dots are a highly attractive alternative for terahertz devices, because of their intrinsic discrete energy levels. Here, we present the first measurements, and theoretical description, of the intersublevel carrier relaxation in quantum dots for transition energies in the few terahertz range. Long intradot relaxation times (1.5 ns) are found for level separations of 14 meV (3.4 THz), decreasing very strongly to ∼2 ps at 30 meV (7 THz), in very good agreement with our microscopic theory of the carrier relaxation process. Our studies pave the way for quantum-dot terahertz device development, providing the fundamental knowledge of carrier relaxation times required for optimum device design.

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Figure 1: Intersublevel transitions in quantum dots.
Figure 2: Population dynamics in quantum dots.
Figure 3: Intersublevel lifetimes in the terahertz region.

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Acknowledgements

Financial support was provided by the UK Engineering and Physical Sciences Research Council (EPSRC). The LPA (UMR 8551) is associated with the CNRS and the Universities Paris 6 and Paris 7. The free-electron laser ‘FELBE’ is supported by the Integrating Activity on Synchrotron and Free-Electron Laser Science (IA-SFS) under the EU contract RII3-CT-2004-506008 of the 6th Framework ‘Structuring the European Research Area, Research Infrastructures Action’. We are grateful to P. Michel and the FELBE team for their dedicated support.

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Author notes

  1. E. A. Zibik, T. Grange & H. Y. Liu

    Present address: Present addresses: Oclaro (Switzerland) AG, Binzstrasse 17, CH-8045 Zürich, Switzerland (E.A.Z.); Walter Schottky Institut, Technische Universität München, 85748 Garching, Germany (T.G.); Department of Electronic & Electrical Engineering, University College London, London WC1E 7JE, UK (H.Y.L.),

  2. E. A. Zibik and T. Grange: These authors contributed equally to this work

Authors and Affiliations

  1. Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK

    E. A. Zibik, B. A. Carpenter, N. E. Porter, M. S. Skolnick & L. R. Wilson

  2. Laboratoire Pierre Aigrain, Ecole Normale Supérieure, Centre National de la Recherche Scientifique, 24 Rue Lhomond, 75005 Paris, France

    T. Grange, R. Ferreira & G. Bastard

  3. Institute of Ion Beam Physics and Material Research, Forschungszentrum Rossendorf, 01314 Dresden, PO Box 510119, Germany

    D. Stehr, S. Winnerl & M. Helm

  4. EPSRC National Centre for III–V Technologies, Sheffield S1 3JD, UK

    H. Y. Liu

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Contributions

E.A.Z. and L.R.W. conceived the experiments; E.A.Z., L.R.W., B.A.C., N.E.P., D.S. and S.W. carried out the experiments; T.G., R.F. and G.B. made the theory and modelled the experiments; E.A.Z. and T.G. analysed the data; L.R.W., R.F., E.A.Z. and M.S.S. supervised the project; H.Y.L. grew the samples; T.G., E.A.Z., R.F. and L.R.W. wrote the paper with major input and edits from M.S.S. and M.H. All authors discussed the results and commented on the manuscript.

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Correspondence to R. Ferreira or L. R. Wilson.

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Zibik, E., Grange, T., Carpenter, B. et al. Long lifetimes of quantum-dot intersublevel transitions in the terahertz range. Nature Mater 8, 803–807 (2009). https://doi.org/10.1038/nmat2511

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