Photoluminescence kinetics of dark and bright excitons in atomically thin MoS${}_2$

Abstract

The fine structure of the exciton spectrum, containing optically allowed (bright) and forbidden (dark) exciton states, determines the radiation efficiency in nanostructures. We study time-resolved micro-photoluminescence in MoS${}_2$ monolayers and bilayers, both unstrained and compressively strained, in a wide temperature range (10-300 K) to distinguish between exciton states optically allowed and forbidden, both in spin and momentum, as well as to estimate their characteristic decay times and contributions to the total radiation intensity. The decay times were found to either increase or decrease with increasing temperature, indicating the lowest bright or lowest dark state, respectively. Our results unambiguously show that, in an unstrained monolayer, the spin-allowed state is the lowest for a series of A excitons (1.9 eV) with the dark state being < 2 meV higher, and that the splitting energy can increase several times at compression. In contrast, in the indirect exciton series in bilayers (1.5 eV), the spin-forbidden state is the lowest, being about 3 meV below the bright one. The strong effect of strain on the exciton spectrum can explain the large scatter among the published data and must be taken into account to realize the desired optical properties of 2D MoS${}_2$.

References in corpus (42)

• Atomically thin MoS2: A new direct-gap semiconductor
• Anomalous Lattice Vibrations of Single and Few-Layer MoS2
• Bandgap Engineering of Strained Monolayer and Bilayer MoS2
• Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material
• Experimental demonstration of continuous electronic structure tuning via strain in atomically thin MoS2
• Low-temperature photocarrier dynamics in monolayer MoS2
• Excitonic linewidth approaching the homogeneous limit in MoS2 based van der Waals heterostructures : accessing spin-valley dynamics
• Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2
• Origin of indirect optical transitions in few-layer MoS2, WS2 and WSe2
• Shear and Layer Breathing Modes in Multilayer MoS2
• Exciton Radiative Lifetime in Transition Metal Dichalcogenide Monolayers
• Strain tuning of optical emission energy and polarization in monolayer and bilayer MoS2
• Magnetic brightening and control of dark excitons in monolayer WSe2
• Carrier and polarization dynamics in monolayer MoS2
• In-plane Propagation of Light in Transition Metal Dichalcogenide Monolayers: Optical Selection Rules
• Charged excitons in monolayer WSe${}_2$: experiment and theory
• Exciton fine structure and spin decoherence in monolayers of transition metal dichalcogenides
• Splitting between Bright and Dark excitons in Transition Metal Dichalcogenide Monolayers
• Brightening of dark excitons in monolayers of semiconducting transition metal dichalcogenides
• Transport Theory of Monolayer Transition-Metal Dichalcogenides through Symmetry
• Exciton band structure in layered MoSe2: from a monolayer to the bulk limit
• Exciton Dynamics in Monolayer Transition Metal Dichalcogenides
• Fine Structure and Lifetime of Dark Excitons in Transition Metal Dichalcogenide Monolayers
• Surface Recombination Limited Lifetimes of Photoexcited Carriers in Few-Layer Transition Metal Dichalcogenide MoS2
• Control of biaxial strain in single-layer Molybdenite using local thermal expansion of the substrate
• Exciton and trion dynamics in atomically thin MoSe2 and WSe2: effect of localization
• Polarization analysis of excitons in monolayer and bilayer transition-metal dichalcogenides
• Direct exciton emission from atomically thin transition metal dichalcogenide heterostructures near the lifetime limit
• Spin and valley dynamics of excitons in transition metal dichalcogenides monolayers
• Spin-flip processes and radiative decay of dark intravalley excitons in transition metal dichalcogenide monolayers
• Probing and manipulating valley coherence of dark excitons in monolayer WSe${}_2$
• Well separated trion and neutral excitons on superacid treated MoS2 monolayers
• Dark trions govern the temperature-dependent optical absorption and emission of doped atomically thin semiconductors
• Strain effects on the spin-orbit induced band structure splittings in monolayer MoS2 and graphene
• Effects of Hexagonal Boron Nitride Encapsulation on the Electronic Structure of Few-layer MoS${}_2$
• Fine structure of $\mathrm{K}$-excitons in multilayers of transition metal dichalcogenides
• Hybrid k$\cdot$p tight-binding model for subbands and infrared intersubband optics in few-layer films of transition-metal dichalcogenides: MoS${}_2$, MoSe${}_2$, WS${}_2$ and WSe${}_2$
• Strain-dependent exciton diffusion in transition metal dichalcogenides
• Excitonic emission in van-der-Waals nanotubes of transition metal dichalcogenides
• Indirect bandgap of hBN-encapsulated monolayer MoS2
• Dark-exciton based strain sensing in transition metal dichalcogenides
• Theory of single and double electron spin-flip Raman scattering in semiconductor nanoplatelets