Direct versus indirect band gap emission and exciton-exciton annihilation in atomically thin molybdenum ditelluride (MoTe${}_2$)

Abstract

We probe the room temperature photoluminescence of $N$-layer molybdenum ditelluride (MoTe${}_2$) in the continuous wave (cw) regime. The photoluminescence quantum yield of monolayer MoTe${}_2$ is three times larger than in bilayer MoTe${}_2$ and forty times greater than in the bulk limit. Mono- and bilayer MoTe${}_2$ display almost symmetric emission lines at $1.10\mathrm{eV}$ and $1.07\mathrm{eV}$, respectively, which predominantly arise from direct radiative recombination of the A exciton. In contrast, $N\ge 3-$layer MoTe${}_2$ exhibits a much reduced photoluminescence quantum yield and a broader, redshifted and seemingly bimodal photoluminescence spectrum. The low- and high-energy contributions are attributed to emission from the indirect and direct optical band gaps, respectively. Bulk MoTe${}_2$ displays a broad emission line with a dominant contribution at 0.94~eV that is assigned to emission from the indirect optical band gap. As compared to related systems (such as MoS${}_2$, MoSe${}_2$, WS${}_2$ and WSe${}_2$), the smaller energy difference between the monolayer direct optical band gap and the bulk indirect optical band gap leads to a smoother increase of the photoluminescence quantum yield as $N$ decreases. In addition, we study the evolution of the photoluminescence intensity in monolayer MoTe${}_2$ as a function of the exciton formation rate $W_{\mathrm{abs}}$ up to $3.6\times 10^{22}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$. The lineshape of the photoluminescence spectrum remains largely independent of $W_{\mathrm{abs}}$, whereas the photoluminescence intensity grows sub-linearly above $W_{\mathrm{abs}}\sim 10^{21}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$. This behavior is assigned to exciton-exciton annihilation and is well-captured by an elementary rate equation model.

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Cited by in corpus (18)

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• Zeeman splitting via spin-valley-layer coupling in bilayer MoTe2
• Excitonic properties of semiconducting monolayer and bilayer MoTe2
• 2D condensate of electrons and holes in ultrathin MoTe${}_2$ photocells
• Exciton states in monolayer MoSe2 and MoTe2 probed by upconversion spectroscopy
• Characterization of Thin Film Materials using SCAN meta-GGA, an Accurate Nonempirical Density Functional
• Room Temperature Valley Polarization and Coherence in Transition Metal Dichalcogenide-Graphene van der Waals Heterostructures
• Quantum interference effects in resonant Raman spectroscopy of single- and triple-layer MoTe${}_2$ from first principles
• Room temperature infrared photodetectors with hybrid structure based on 2D materials
• Light-tunable charge density wave orders in MoTe2 and WTe2 single layers
• MoTe2 as a natural hyperbolic material across the visible and the ultraviolet region
• Luminescence anomaly of dipolar valley excitons in homobilayer semiconductor moiré superlattices
• Annihilation mechanism of excitons in a MoS2 monolayer through direct Förster-type energy transfer and multistep diffusion
• Correlating the Electronic Structures of Metallic/Semiconductor MoTe2 Interface to its Atomic Structures
• Hybrid moiré excitons and trions in twisted MoTe${}_2$-MoSe${}_2$ heterobilayers
• Kinetic mechanism for reversible structural transition in MoTe2 induced by excess charge carriers
• Microring Resonators Coupling Tunability by Heterogeneous 2D Material Integration