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Metal–insulator transition in films of doped semiconductor nanocrystals

Nature Materials volume 15, pages 299–303 (2016)Cite this article

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Abstract

To fully deploy the potential of semiconductor nanocrystal films as low-cost electronic materials, a better understanding of the amount of dopants required to make their conductivity metallic is needed. In bulk semiconductors, the critical concentration of electrons at the metal–insulator transition is described by the Mott criterion. Here, we theoretically derive the critical concentration nc for films of heavily doped nanocrystals devoid of ligands at their surface and in direct contact with each other. In the accompanying experiments, we investigate the conduction mechanism in films of phosphorus-doped, ligand-free silicon nanocrystals. At the largest electron concentration achieved in our samples, which is half the predicted nc, we find that the localization length of hopping electrons is close to three times the nanocrystals diameter, indicating that the film approaches the metal–insulator transition.

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Figure 1: The origin of the metal-to-insulator transition in semiconductor nanocrystal films.
Figure 2: Determining the free carrier density from the localized surface plasmon resonance.
Figure 3: Electrical transport in phosphorous-doped Si NC films approaching the metal-to-insulator transition.

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Acknowledgements

The authors would like to thank K. A. Matveev, C. Leighton, B. Skinner and A. Kamenev for helpful discussions, C. D. Frisbie for the use of his equipment and R. Knurr for assistance with the ICP-OES analysis. T.C. (electrical transport studies) and K.V.R.(theory) were supported primarily by the National Science Foundation through the University of Minnesota MRSEC under Award Number DMR-1420013. N.J.K. (materials synthesis) was supported by the DOE Center for Advanced Solar Photophysics (CASP), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Part of this work was carried out in the College of Science and Engineering Characterization Facility, University of Minnesota, which has received capital equipment funding from the NSF through the UMN MRSEC Program. Part of this work also used the College of Science and Engineering Nanofabrication Center, University of Minnesota, which receives partial support from NSF through the NNIN Program.

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Authors and Affiliations

  1. Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA

    Ting Chen

  2. Fine Theoretical Physics Institute, University of Minnesota, Minneapolis, Minnesota 55455, USA

    K. V. Reich, Han Fu & B. I. Shklovskii

  3. Ioffe Institute, St Petersburg 194021, Russia

    K. V. Reich

  4. Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota 55455, USA

    Nicolaas J. Kramer & Uwe R. Kortshagen

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  1. Ting Chen
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  2. K. V. Reich
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  4. Han Fu
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  5. Uwe R. Kortshagen
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  6. B. I. Shklovskii
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Contributions

K.V.R., H.F. and B.I.S. created the theory. T.C. performed the structural and electrical characterization. N.J.K. synthesized materials. U.R.K. discussed and supervised the work. All authors participated in the discussion and interpretation of the results and co-wrote the manuscript.

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Correspondence to B. I. Shklovskii.

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Chen, T., Reich, K., Kramer, N. et al. Metal–insulator transition in films of doped semiconductor nanocrystals. Nature Mater 15, 299–303 (2016). https://doi.org/10.1038/nmat4486

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