Probing excitonic states in ultraclean 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 <1ms) photoresponse combined with the high quality of our devices 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 estimate an extremely large binding energy for band-edge excitons, Ebind > 570meV. 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.

12 pages, 4 figures

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Cited by in corpus (28)

• Computational 2D Materials Database: Electronic Structure of Transition-Metal Dichalcogenides and Oxides
• k.p theory for two-dimensional transition metal dichalcogenide semiconductors
• Photocurrent generation with two-dimensional van der Waals semiconductors
• Non-linear Optical Spectroscopy of Excited Exciton States for Efficient Valley Coherence Generation in WSe2 Monolayers
• Brightening of dark excitons in monolayers of semiconducting transition metal dichalcogenides
• Micro-reflectance and transmittance spectroscopy: a versatile and powerful tool to characterize 2D materials
• Polarization and time-resolved photoluminescence spectroscopy of excitons in MoSe2 monolayers
• Magneto-optics in transition metal diselenide monolayers
• Electrical control of near-field energy transfer between quantum dots and 2D semiconductors
• Three-particle Complexes in Two-Dimensional Semiconductors
• Optically discriminating carrier-induced quasiparticle band gap and exciton energy renormalization in monolayer MoS2
• Giant Valley-Zeeman Splitting from Spin-Singlet and Spin-Triplet Interlayer Excitons in WSe2/MoSe2 Heterostructure
• Intrinsic exciton states mixing and non-linear optical properties in transition metal dichalcogenide monolayers
• Magneto-photoluminescence of exciton Rydberg states in monolayer WSe${}_2$
• Electrically tunable organic-inorganic hybrid polaritons with monolayer WS2
• Excitons and trions in monolayer transition metal dichalcogenides: A comparative study between the multiband model and the quadratic single-band model
• Influence of the effective layer thickness on the groundstate and excitonic properties of transition-metal dichalcogenide systems
• Photoresponse of Natural van der Waals Heterostructures
• Nonlinear optical selection rules of excitons in monolayer transition metal dichalcogenides
• Simple vertex correction improves GW band energies of bulk and two-dimensional crystals
• Scalable Fabrication of Atomically Thin Monolayer MoS2 Photodetectors
• Spin-resolved optical conductivity of two-dimensional group-VIB transition-metal dichalcogenides
• Valley-Polarized Exciton Dynamics in Exfoliated Monolayer WSe${}_2$
• Visualization of defect-induced excitonic properties of the edges and grain boundaries in synthesized monolayer molybdenum disulfide
• Semiconductor channel mediated photodoping in h-BN encapsulated monolayer MoSe2 phototransistors
• Photodetection in p-n junctions formed by electrolyte-gated transistors of two-dimensional crystals
• Excitation energy dependence of Raman spectra of few-layer WS2
• Ultrafast Insight into High energy (C, D) Excitons in Few Layer WS2