Article | Published:

Photoexcitation cascade and multiple hot-carrier generation in graphene

Nature Physics volume 9, pages 248252 (2013) | Download Citation


The conversion of light into free electron–hole pairs constitutes the key process in the fields of photodetection and photovoltaics. The efficiency of this process depends on the competition of different relaxation pathways and can be greatly enhanced when photoexcited carriers do not lose energy as heat, but instead transfer their excess energy into the production of additional electron–hole pairs through carrier–carrier scattering processes. Here we use optical pump–terahertz probe measurements to probe different pathways contributing to the ultrafast energy relaxation of photoexcited carriers. Our results indicate that carrier–carrier scattering is highly efficient, prevailing over optical-phonon emission in a wide range of photon wavelengths and leading to the production of secondary hot electrons originating from the conduction band. As hot electrons in graphene can drive currents, multiple hot-carrier generation makes graphene a promising material for highly efficient broadband extraction of light energy into electronic degrees of freedom, enabling high-efficiency optoelectronic applications.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1.

    et al. Fine structure constant defines visual transparency of graphene. Science 320, 1308 (2008).

  2. 2.

    et al. Electron–electron interactions in graphene: Current status and perspectives. Rev. Mod. Phys. 84, 1067–1125 (2012).

  3. 3.

    , , & Graphene photonics and optoelectronics. Nature Photon. 4, 611–622 (2010).

  4. 4.

    , & Carrier multiplication in graphene. Nano Lett. 10, 4839–4843 (2010).

  5. 5.

    & Impact of Auger processes on carrier dynamics in graphene. Phys. Rev. B 85, 241404 (2012).

  6. 6.

    et al. Hot carrier assisted intrinsic photoresponse in graphene. Science 334, 648–652 (2011).

  7. 7.

    et al. Hot carrier transport and photocurrent response in graphene. Nano Lett. 11, 4688–4692 (2011).

  8. 8.

    et al. Assessment of carrier-multiplication efficiency in bulk PbSe and PbS. Nature Phys. 5, 811–814 (2009).

  9. 9.

    et al. Carrier multiplication and its reduction by photodoping in colloidal InAs quantum dots. J. Phys. Chem. C 111, 4146–4152 (2007).

  10. 10.

    & High efficiency carrier multiplication in PbSe nanocrystals: Implications for solar energy conversion. Phys. Rev. Lett. 92, 186601 (2004).

  11. 11.

    , & High-efficiency carrier multiplication through direct photogeneration of multi-excitons via virtual single–exciton states. Nature Phys. 1, 189–194 (2005).

  12. 12.

    et al. Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy. Rev. Mod. Phys. 83, 543–586 (2011).

  13. 13.

    et al. Ultrafast optical-pump terahertz-probe spectroscopy of the carrier relaxation and recombination dynamics in epitaxial graphene. Nano Lett. 8, 4248–4251 (2008).

  14. 14.

    et al. Very slow cooling dynamics of photoexcited carriers in graphene observed by optical-pump terahertz-probe spectroscopy. Nano Lett. 11, 4902–4906 (2011).

  15. 15.

    et al. Carrier relaxation in epitaxial graphene photoexcited near the Dirac point. Phys. Rev. Lett. 107, 237401 (2011).

  16. 16.

    , & Ultrafast carrier dynamics in graphite. Phys. Rev. Lett. 102, 086809 (2009).

  17. 17.

    et al. Ultrafast nonequilibrium carrier dynamics in a single graphene layer. Phys. Rev. B 83, 153410 (2011).

  18. 18.

    et al. Strongly coupled optical phonons in the ultrafast dynamics of the electronic energy and current relaxation in graphite. Phys. Rev. Lett. 95, 187403 (2005).

  19. 19.

    et al. Nonlinear THz conductivity dynamics in CVD-grown graphene. Preprint  (2011).

  20. 20.

    et al. Observation of suppressed THz absorption in photoexcited graphene. Preprint  (2013).

  21. 21.

    & Quantum Hall ferromagnetism in graphene. Phys. Rev. Lett. 96, 256602 (2006).

  22. 22.

    Screening effect and impurity scattering in monolayer graphene. J. Phys. Soc. Jpn 75, 074716 (2006).

  23. 23.

    , , & Electronic transport in two-dimensional graphene. Rev. Mod. Phys. 83, 407–470 (2011).

  24. 24.

    et al. Photo-excited carrier dynamics and impact excitation cascade in graphene. Preprint .

  25. 25.

    & Electronic cooling in graphene. Phys. Rev. Lett. 102, 206410 (2009).

  26. 26.

    & Energy relaxation of hot Dirac fermions in graphene. Phys. Rev. B 79, 235406 (2009).

  27. 27.

    , & Disorder-assisted electron phonon scattering and cooling pathways in graphene. Phys. Rev. Lett. 109, 106602 (2012).

  28. 28.

    & Slow imbalance relaxation and thermoelectric transport in graphene. Phys. Rev. B 79, 085415 (2009).

Download references


We acknowledge financial support from an NWO Rubicon grant (K.J.T.), the NSS programme, Singapore (J.C.W.S.), Office of Naval Research Grant No. N00014-09-1-0724 (L.S.L.), and Fundacio Cellex Barcelona and ERC Career integration grant GRANOP (F.H.L.K.). We thank J. Versluis for technical assistance.

Author information


  1. ICFO—Institut de Ciéncies Fotóniques, Mediterranean Technology Park, Castelldefels (Barcelona) 08860, Spain

    • K. J. Tielrooij
    •  & F. H. L. Koppens
  2. Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • J. C. W. Song
    •  & L. S. Levitov
  3. School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA

    • J. C. W. Song
  4. Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany

    • S. A. Jensen
    •  & M. Bonn
  5. FOM Institute AMOLF, Amsterdam, Science Park 104, 1098 XG Amsterdam, Netherlands

    • S. A. Jensen
  6. Graphenea SA, 20018 Donostia-San Sebastián, Spain

    • A. Centeno
    • , A. Pesquera
    •  & A. Zurutuza Elorza


  1. Search for K. J. Tielrooij in:

  2. Search for J. C. W. Song in:

  3. Search for S. A. Jensen in:

  4. Search for A. Centeno in:

  5. Search for A. Pesquera in:

  6. Search for A. Zurutuza Elorza in:

  7. Search for M. Bonn in:

  8. Search for L. S. Levitov in:

  9. Search for F. H. L. Koppens in:


K.J.T., F.H.L.K. and M.B. conceived the experiment; K.J.T. and S.A.J. performed the experiment; K.J.T., J.C.W.S., L.S.L. and F.H.L.K. analysed and interpreted the data; J.C.W.S. and L.S.L. developed the theoretical model; A.C., A.P. and A.Z.E. prepared the sample; K.J.T., J.C.W.S., S.A.J., M.B., L.S.L. and F.H.L.K. wrote the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to K. J. Tielrooij or F. H. L. Koppens.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    Supplementary Information

About this article

Publication history





Further reading