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Highly anisotropic and robust excitons in monolayer black phosphorus

Nature Nanotechnology volume 10, pages 517–521 (2015)Cite this article

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Abstract

Semi-metallic graphene and semiconducting monolayer transition-metal dichalcogenides are the most intensively studied two-dimensional materials of recent years1,2. Lately, black phosphorus has emerged as a promising new two-dimensional material due to its widely tunable and direct bandgap, high carrier mobility and remarkable in-plane anisotropic electrical, optical and phonon properties3,4,5,6,7,8,9. However, current progress is primarily limited to its thin-film form. Here, we reveal highly anisotropic and strongly bound excitons in monolayer black phosphorus using polarization-resolved photoluminescence measurements at room temperature. We show that, regardless of the excitation laser polarization, the emitted light from the monolayer is linearly polarized along the light effective mass direction and centres around 1.3 eV, a clear signature of emission from highly anisotropic bright excitons. Moreover, photoluminescence excitation spectroscopy suggests a quasiparticle bandgap of 2.2 eV, from which we estimate an exciton binding energy of ∼0.9 eV, consistent with theoretical results based on first principles. The experimental observation of highly anisotropic, bright excitons with large binding energy not only opens avenues for the future explorations of many-electron physics in this unusual two-dimensional material, but also suggests its promising future in optoelectronic devices.

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Figure 1: Characterization of monolayer black phosphorus.
Figure 2: Exciton photoluminescence with large in-plane anisotropy.
Figure 3: Large exciton binding energy revealed by PLE spectroscopy.

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Acknowledgements

This work was mainly supported by the Office of Naval Research (N00014-14-1-0565). M.J., K.S. and X.X. are supported by the Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division (DE-SC0008145 and DE-SC0012509). H.Z. and H.W. are supported by Army Research Laboratory (W911NF-14-2-0113). The use of facilities in Yale was supported by Yale Institute for Nanoscience and Quantum Engineering (YINQE) and the National Science Foundation (MRSEC DMR-1119826). The UW facility is partially supported by the State of Washington through the University of Washington Clean Energy Institute. V.T. and L.Y. are supported by the National Science Foundation (DMR-1207141). The authors acknowledge Mildred Dresselhaus at Massachusetts Institute of Technology for helpful comments during the preparation of the manuscript.

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Authors and Affiliations

  1. Department of Electrical Engineering, Yale University, New Haven, 06511, Connecticut, USA

    Xiaomu Wang, Yichen Jia & Fengnian Xia

  2. Department of Physics and Department of Materials Science and Engineering, University of Washington, Seattle, 98195, Washington, USA

    Aaron M. Jones, Kyle L. Seyler & Xiaodong Xu

  3. Department of Physics, Washington University, St Louis, 63130, Missouri, USA

    Vy Tran & Li Yang

  4. Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, 90089, California, USA

    Huan Zhao & Han Wang

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  1. Xiaomu Wang
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Contributions

F.X., X.W. and H.W. conceived the projects. X.W. prepared samples and carried out Raman measurements. A.M.J., K.L.S. and X.W. performed photoluminescence measurements. V.T. and L.Y. performed the density functional theory calculations. Y.J. and H.Z. helped with sample preparation. F.X. and X.W. wrote the manuscript with input from L.Y., X.X. and H.W. F.X. and X.X. supervised the project. All authors discussed the results and commented on the manuscript.

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Correspondence to Xiaodong Xu or Fengnian Xia.

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The authors declare no competing financial interests.

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Wang, X., Jones, A., Seyler, K. et al. Highly anisotropic and robust excitons in monolayer black phosphorus. Nature Nanotech 10, 517–521 (2015). https://doi.org/10.1038/nnano.2015.71

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