Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Contact and edge effects in graphene devices

Nature Nanotechnology volume 3, pages 486–490 (2008)Cite this article

Abstract

Electrical transport studies on graphene have been focused mainly on the linear dispersion region around the Fermi level1,2 and, in particular, on the effects associated with the quasiparticles in graphene behaving as relativistic particles known as Dirac fermions3,4,5. However, some theoretical work has suggested that several features of electron transport in graphene are better described by conventional semiconductor physics6,7. Here we use scanning photocurrent microscopy to explore the impact of electrical contacts and sheet edges on charge transport through graphene devices. The photocurrent distribution reveals the presence of potential steps that act as transport barriers at the metal contacts. Modulations in the electrical potential within the graphene sheets are also observed. Moreover, we find that the transition from the p- to n-type regime induced by electrostatic gating does not occur homogeneously within the sheets. Instead, at low carrier densities we observe the formation of p-type conducting edges surrounding a central n-type channel.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Photocurrent response of a graphene device.
Figure 2: Spatially resolved photocurrent maps at various transport regimes of a graphene device.
Figure 3: Quantitative determination of the potential steps at the metal–graphene interface.
Figure 4: Invasive nature of metal contacts to graphene.

Similar content being viewed by others

References

  1. Novoselov, K. S. et al. Electric field effect in atomically thin carbon films. Science 306, 666–669 (2004).

    Article  Google Scholar 

  2. Geim, A. K. & Novoselov, K. S. The rise of graphene. Nature Mater. 6, 183–191 (2007).

    Article  Google Scholar 

  3. Novoselov, K. S. et al. Two-dimensional gas of massless Dirac fermions in graphene. Nature 438, 197–200 (2005).

    Article  Google Scholar 

  4. Zhang, Y., Tan, J. W., Stormer, H. L. & Kim, P. Experimental observation of the quantum Hall effect and Berry's phase in graphene. Nature 438, 201–204 (2005).

    Article  Google Scholar 

  5. Katsnelson, M. I., Novoselov, K. S. & Geim, A. K. Chiral tunneling and the Klein paradox in graphene. Nature Phys. 2, 620–625 (2006).

    Article  Google Scholar 

  6. Hwang, E. H., Adam, S. & Das Sarma, S. Carrier transport in two-dimensional graphene layers. Phys. Rev. Lett. 98, 186806 (2007).

    Article  Google Scholar 

  7. Adam, S., Hwang, E. H., Galitski, V. M. & Das Sarma, S. A self-consistent theory for graphene transport. Proc. Natl Acad. Sci. USA 104, 18392–18397 (2007).

    Article  Google Scholar 

  8. Martin, J. et al. Observation of electron–hole puddles in graphene using a scanning single-electron transistor. Nature Phys. 4, 144–148 (2008).

    Article  Google Scholar 

  9. Tan, Y. W. et al. Measurement of scattering rate and minimum conductivity in graphene. Phys. Rev. Lett. 99, 246803 (2007).

    Article  Google Scholar 

  10. Rossi, E. & Das Sarma, S. Ground-state of graphene in the presence of random charge impurities. Preprint at <http://arxiv.org/abs/0803.0963> (2008).

  11. Polini, M., Tomadin, A., Asgari, R. & MacDonald, A. H. Density-functional theory of graphene sheets. Preprint at <http://arxiv.org/abs/0803.4150> (2008).

  12. Sze, S. M. Physics of Semiconductor Devices (Wiley, New York, 2007).

  13. Giovannetti, G. et al. Doping graphene with metal contacts. Preprint at <http://arxiv.org/abs/0802.2267v2> (2008).

  14. Golizadeh-Mojarad, R. & Datta, S. Effect of the contact induced states on minimum conductivity in graphene. Preprint at <http://arxiv.org/abs/0710.2727> (2007).

  15. Huard, B., Stander, N., Sulpizio, J. A. & Goldhaber-Gordon, D. Evidence of the role of contacts on the observed electron–hole symmetry in graphene. Preprint at <http://arxiv.org/abs/0804.2040v1> (2008).

  16. Balasubramanian, K. et al. Photoelectronic transport imaging of individual semiconducting carbon nanotubes. Appl. Phys. Lett. 84, 2400–2402 (2004).

    Article  Google Scholar 

  17. Balasubramanian, K., Burghard, M., Kern, K., Scolari, M. & Mews, A. Photocurrent imaging of charge transport barriers in carbon nanotube devices. Nano Lett. 5, 507–510 (2005).

    Article  Google Scholar 

  18. Lee, E. J. H. et al. Electronic band structure mapping of nanotube transistors by scanning photocurrent microscopy. Small 3, 2038–2042 (2007).

    Article  Google Scholar 

  19. Freitag, M. et al. Imaging of the Schottky barriers and charge depletion in carbon nanotube transistors. Nano Lett. 7, 2037–2042 (2007).

    Article  Google Scholar 

  20. Ahn, Y., Dunning, J. & Park, J. Scanning photocurrent imaging and electronic band studies in silicon nanowire field effect transistors. Nano Lett. 5, 1367–1370 (2005).

    Article  Google Scholar 

  21. Ferrari, A. C. et al. Raman spectrum of graphene and graphene layers. Phys. Rev. Lett. 97, 187401 (2006).

    Article  Google Scholar 

  22. Horcas, I. et al. WSxM: a software for scanning probe microscopy and a tool for nanotechnology. Rev. Sci. Instrum. 78, 013705 (2007).

    Article  Google Scholar 

  23. Graf, D. et al. Spatially-resolved Raman spectroscopy of single- and few-layer graphene. Nano Lett. 7, 238–242 (2007).

    Article  Google Scholar 

  24. Blake, P. et al. Making graphene visible. Appl. Phys. Lett. 91, 063124 (2007).

    Article  Google Scholar 

  25. Roddaro, S., Pingue, P., Piazza, V., Pellegrini, V. & Beltram, F. The optical visibility of graphene: interference colours of ultrathin graphite on SiO2 . Nano Lett. 7, 2707–2710 (2007).

    Article  Google Scholar 

  26. Piscanec, S., Lazzeri, M., Mauri, F., Ferrari, A. C. & Robertson, J. Kohn anomalies and electron–phonon interactions in graphite. Phys. Rev. Lett. 93, 185503 (2004).

    Article  Google Scholar 

  27. Hansen, W. N. & Johnson, K. B. Work function measurements in gas ambient. Surf. Sci. 316, 373–382 (1994).

    Article  Google Scholar 

  28. Klusek, Z. et al. Local electronic edge states of graphene layer deposited on Ir(111) surface studied by STM/CITS. Appl. Surf. Sci. 252, 1221–1227 (2005).

    Article  Google Scholar 

Download references

Acknowledgements

The authors gratefully thank J. Smet and D. Obergfell for help with the preparation of the graphene monolayers, and A. Forment-Aliaga and A. Sagar for the Raman spectroscopy measurements.

Author information

Authors and Affiliations

  1. Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, Stuttgart, D-70569, Germany

    Eduardo J. H. Lee, Kannan Balasubramanian, Ralf Thomas Weitz, Marko Burghard & Klaus Kern

  2. Institut de Physique des Nanostructures, École Polytechnique Fédérale de Lausanne, Lausanne, CH-1015, Switzerland

    Klaus Kern

Authors
  1. Eduardo J. H. Lee
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Kannan Balasubramanian
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Ralf Thomas Weitz
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Marko Burghard
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Klaus Kern
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Eduardo J. H. Lee.

Supplementary information

Rights and permissions

Reprints and permissions

About this article

Cite this article

Lee, E., Balasubramanian, K., Weitz, R. et al. Contact and edge effects in graphene devices. Nature Nanotech 3, 486–490 (2008). https://doi.org/10.1038/nnano.2008.172

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nnano.2008.172

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing