Unusually large exciton binding energy in multilayered 2H-MoTe2

Abstract

Although large exciton binding energies of typically 0.6–1.0 eV are observed for monolayer transition metal dichalcogenides (TMDs) owing to strong Coulomb interaction, multilayered TMDs yield relatively low exciton binding energies owing to increased dielectric screening. Recently, the ideal carrier-multiplication threshold energy of twice the bandgap has been realized in multilayered semiconducting 2H-MoTe2 with a conversion efficiency of 99%, which suggests strong Coulomb interaction. However, the origin of strong Coulomb interaction in multilayered 2H-MoTe2, including the exciton binding energy, has not been elucidated to date. In this study, unusually large exciton binding energy is observed through optical spectroscopy conducted on CVD-grown 2H-MoTe2. To extract exciton binding energy, the optical conductivity is fitted using the Lorentz model to describe the exciton peaks and the Tauc–Lorentz model to describe the indirect and direct bandgaps. The exciton binding energy of 4 nm thick multilayered 2H-MoTe2 is approximately 300 meV, which is unusually large by one order of magnitude when compared with other multilayered TMD semiconductors such as 2H-MoS2 or 2H-MoSe2. This finding is interpreted in terms of small exciton radius based on the 2D Rydberg model. The exciton radius of multilayered 2H-MoTe2 resembles that of monolayer 2H-MoTe2, whereas those of multilayered 2H-MoS2 and 2H-MoSe2 are large when compared with monolayer 2H-MoS2 and 2H-MoSe2. From the large exciton binding energy in multilayered 2H-MoTe2, it is expected to realize the future applications such as room-temperature and high-temperature polariton lasing.

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Electrically Modulated Single/Multicolor High Responsivity 2D MoTe2/MoS2 Photodetector for Broadband Detection

“…The responsivity of the NIR-IR region decreases as the bias is increased to a positive value (Figure 4d). The thicker the MoTe 2 , the lower the exciton binding energy owing to the dielectric screening effect, 30 and the separation efficiency of the excitons decreases as the bias increases to positive. In particular, at a bias voltage of +3 V, the excitons in MoTe 2 cannot separate the photogenerated electron−hole pairs because of the reduced electric field strength and valence band offset of the MoTe 2 /MoS 2 heterostructure.…”

Self-Assembled Monolayer Doping for MoTe2 Field-Effect Transistors: Overcoming PN Doping Challenges in Transition Metal Dichalcogenides

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