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Nat Nanotechnol. 2015 Jun;10(6):517-21. doi: 10.1038/nnano.2015.71. Epub 2015 Apr 27.

Highly anisotropic and robust excitons in monolayer black phosphorus.

Author information

1
Department of Electrical Engineering, Yale University, New Haven, Connecticut 06511, USA.
2
Department of Physics and Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, USA.
3
Department of Physics, Washington University, St Louis, Missouri 63130, USA.
4
Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, USA.

Abstract

Semi-metallic graphene and semiconducting monolayer transition-metal dichalcogenides are the most intensively studied two-dimensional materials of recent years. 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 properties. 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.

PMID:
25915195
DOI:
10.1038/nnano.2015.71

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