Unusually large exciton binding energy in multilayered 2H-MoTe₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Monolayer transition metal dichalcogenides (TMDs) exhibit high exciton binding energies (0.6-1.0 eV) due to strong Coulomb interaction.
• Multilayered TMDs typically show reduced exciton binding energies because of increased dielectric screening.
• Recent studies in multilayered 2H-MoTe2 demonstrated ideal carrier-multiplication, implying strong Coulomb interaction, but its origin remained unclear.

Purpose of the Study:

• To investigate the origin of strong Coulomb interaction and elucidate the exciton binding energy in multilayered 2H-MoTe2.
• To determine the exciton binding energy in CVD-grown multilayered 2H-MoTe2 using optical spectroscopy.
• To compare the exciton properties of multilayered 2H-MoTe2 with other TMDs.

Main Methods:

• Optical spectroscopy was employed to study CVD-grown multilayered 2H-MoTe2.
• The Lorentz model was used to fit exciton peaks in the optical conductivity.
• The Tauc-Lorentz model was applied to describe the indirect and direct bandgaps.

Main Results:

• Unusually large exciton binding energy of approximately 300 meV was observed in 4 nm thick multilayered 2H-MoTe2.
• This binding energy is an order of magnitude larger than that of other multilayered TMDs (e.g., 2H-MoS2, 2H-MoSe2).
• The small exciton radius in multilayered 2H-MoTe2, similar to its monolayer form, explains the large binding energy, consistent with the 2D Rydberg model.

Conclusions:

• The findings reveal strong Coulomb interaction in multilayered 2H-MoTe2, contrary to expectations based on dielectric screening.
• The observed large exciton binding energy is attributed to a small exciton radius.
• This characteristic is promising for future applications, including room-temperature and high-temperature polariton lasing.