title: Probing excitonic states in suspended two-dimensional semiconductors by photocurrent spectroscopy.
abstract: The optical response of semiconducting monolayer transition-metal dichalcogenides (TMDCs) is dominated by strongly bound excitons that are stable even at room temperature. However, substrate-related effects such as screening and disorder in currently available specimens mask many anticipated physical phenomena and limit device applications of TMDCs. Here, we demonstrate that that these undesirable effects are strongly suppressed in suspended devices. Extremely robust (photogain > 1,000) and fast (response time < 1 ms) photoresponse allow us to study, for the first time, the formation, binding energies, and dissociation mechanisms of excitons in TMDCs through photocurrent spectroscopy. By analyzing the spectral positions of peaks in the photocurrent and by comparing them with first-principles calculations, we obtain binding energies, band gaps and spin-orbit splitting in monolayer TMDCs. For monolayer MoS2, in particular, we obtain an extremely large binding energy for band-edge excitons, E bind ≥ 570 meV. Along with band-edge excitons, we observe excitons associated with a van Hove singularity of rather unique nature. The analysis of the source-drain voltage dependence of photocurrent spectra reveals exciton dissociation and photoconversion mechanisms in TMDCs.
authors.affiliation: Department of Physics and Astronomy, Vanderbilt University, Nashville, TN-37235, USA.
authors.forename: A R
authors.initials: AR
authors.lastname: Klots
authors.affiliation: Department of Physics and Astronomy, Vanderbilt University, Nashville, TN-37235, USA.
authors.forename: A K M
authors.initials: AK
authors.lastname: Newaz
authors.affiliation: Department of Physics and Astronomy, Vanderbilt University, Nashville, TN-37235, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Wang
authors.affiliation: Interdisciplinary Graduate Program in Materials Science, Vanderbilt University, Nashville, TN-37234, USA.
authors.forename: D
authors.initials: D
authors.lastname: Prasai
authors.affiliation: Department of Physics and Astronomy, Vanderbilt University, Nashville, TN-37235, USA.
authors.forename: H
authors.initials: H
authors.lastname: Krzyzanowska
authors.affiliation: 1] Department of Physics and Astronomy, Vanderbilt University, Nashville, TN-37235, USA [2] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN-37831, USA.
authors.forename: Junhao
authors.initials: J
authors.lastname: Lin
authors.affiliation: Department of Physics and Astronomy, Vanderbilt University, Nashville, TN-37235, USA.
authors.forename: D
authors.initials: D
authors.lastname: Caudel
authors.affiliation: 1] Department of Physics and Astronomy, University of Tennessee, Knoxville, TN-37996, USA [2] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN-37831, USA.
authors.forename: N J
authors.initials: NJ
authors.lastname: Ghimire
authors.affiliation: 1] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN-37831, USA [2] Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN-37996, USA.
authors.forename: J
authors.initials: J
authors.lastname: Yan
authors.affiliation: Department of Physics and Astronomy, Vanderbilt University, Nashville, TN-37235, USA.
authors.forename: B L
authors.initials: BL
authors.lastname: Ivanov
authors.affiliation: Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM-87545, USA.
authors.forename: K A
authors.initials: KA
authors.lastname: Velizhanin
authors.affiliation: Department of Physics, Fisk University, Nashville, TN-37208, USA.
authors.forename: A
authors.initials: A
authors.lastname: Burger
authors.affiliation: 1] Department of Physics and Astronomy, University of Tennessee, Knoxville, TN-37996, USA [2] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN-37831, USA [3] Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN-37996, USA.
authors.forename: D G
authors.initials: DG
authors.lastname: Mandrus
authors.affiliation: Department of Physics and Astronomy, Vanderbilt University, Nashville, TN-37235, USA.
authors.forename: N H
authors.initials: NH
authors.lastname: Tolk
authors.affiliation: 1] Department of Physics and Astronomy, Vanderbilt University, Nashville, TN-37235, USA [2] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN-37831, USA.
authors.forename: S T
authors.initials: ST
authors.lastname: Pantelides
authors.affiliation: Department of Physics and Astronomy, Vanderbilt University, Nashville, TN-37235, USA.
authors.forename: K I
authors.initials: KI
authors.lastname: Bolotin