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Nat Mater. 2014 Dec;13(12):1091-5. doi: 10.1038/nmat4061. Epub 2014 Aug 31.

Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor.

Author information

1
1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2].
2
1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2] Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
3
1] Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [2] Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
4
1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2] State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China.
5
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
6
1] Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA [2] Geballe Laboratory for Advanced Materials, Departments of Physics and Applied Physics, Stanford University, Stanford, California 94305, USA.
7
1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2] Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [3] Kavli Energy NanoSciences Institute at the University of California Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are emerging as a new platform for exploring 2D semiconductor physics. Reduced screening in two dimensions results in markedly enhanced electron-electron interactions, which have been predicted to generate giant bandgap renormalization and excitonic effects. Here we present a rigorous experimental observation of extraordinarily large exciton binding energy in a 2D semiconducting TMD. We determine the single-particle electronic bandgap of single-layer MoSe2 by means of scanning tunnelling spectroscopy (STS), as well as the two-particle exciton transition energy using photoluminescence (PL) spectroscopy. These yield an exciton binding energy of 0.55 eV for monolayer MoSe2 on graphene—orders of magnitude larger than what is seen in conventional 3D semiconductors and significantly higher than what we see for MoSe2 monolayers in more highly screening environments. This finding is corroborated by our ab initio GW and Bethe-Salpeter equation calculations which include electron correlation effects. The renormalized bandgap and large exciton binding observed here will have a profound impact on electronic and optoelectronic device technologies based on single-layer semiconducting TMDs.

PMID:
25173579
DOI:
10.1038/nmat4061

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