Layer number dependence of MoS2 photoconductivity using photocurrent spectral atomic force microscopic imaging

Youngwoo Son, Qing Wang, Joel A. Paulson, Chih Jen Shih, Ananth G. Rajan, Kevin Tvrdy, Sojin Kim, Bassam Alfeeli, Richard D. Braatz, Michael S. Strano

Research output: Contribution to journalArticle

49 Scopus citations

Abstract

Atomically thin MoS2 is of great interest for electronic and optoelectronic applications because of its unique two-dimensional (2D) quantum confinement; however, the scaling of optoelectronic properties of MoS2 and its junctions with metals as a function of layer number as well the spatial variation of these properties remain unaddressed. In this work, we use photocurrent spectral atomic force microscopy (PCS-AFM) to image the current (in the dark) and photocurrent (under illumination) generated between a biased PtIr tip and MoS2 nanosheets with thickness ranging between n = 1 to 20 layers. Dark current measurements in both forward and reverse bias reveal characteristic diode behavior well-described by Fowler-Nordheim tunneling with a monolayer barrier energy of 0.61 eV and an effective barrier scaling linearly with layer number. Under illumination at 600 nm, the photocurrent response shows a marked decrease for layers up to n = 4 but increasing thereafter, which we describe using a model that accounts for the linear barrier increase at low n, but increased light absorption at larger n creating a minimum at n = 4. Comparative 2D Fourier analysis of physical height and photocurrent images shows high spatial frequency spatial variations in substrate/MoS2 contact that exceed the frequencies imposed by the underlying substrates. These results should aid in the design and understanding of optoelectronic devices based on quantum confined atomically thin MoS2.

Original languageEnglish (US)
Pages (from-to)2843-2855
Number of pages13
JournalACS nano
Volume9
Issue number3
DOIs
StatePublished - Mar 24 2015

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Keywords

  • MoS
  • conductive AFM
  • layered dichalcogenide
  • metal-MoS junction
  • photoconductive AFM
  • photoconductivity

ASJC Scopus subject areas

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

Cite this

Son, Y., Wang, Q., Paulson, J. A., Shih, C. J., Rajan, A. G., Tvrdy, K., Kim, S., Alfeeli, B., Braatz, R. D., & Strano, M. S. (2015). Layer number dependence of MoS2 photoconductivity using photocurrent spectral atomic force microscopic imaging. ACS nano, 9(3), 2843-2855. https://doi.org/10.1021/nn506924j