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Published on: December 5, 2015
Effects of Interlayer Coupling and Band Offset on Second Harmonic Generation in Vertical MoS2/MoS2(1-Se2 Structures
Chinh Tam Le1, Jungcheol Kim2, Farman Ullah1
1Department of Physics and Energy Harvest Storage Research Center, University of Ulsan, Ulsan 44610, South Korea.
Interlayer coupling in transition metal dichalcogenide (TMDC) bilayers significantly alters second harmonic generation (SHG) by modifying electronic bands. Postannealing TMDC vertical heterostructures enhances SHG, enabling efficient broadband applications.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Nonlinear Optics
Background:
- Noncentrosymmetric transition metal dichalcogenide (TMDC) monolayers and their 3R-type vertical stacks are ideal for studying atomic-scale nonlinear light-matter interactions, particularly second harmonic generation (SHG).
- SHG in TMDC stacks is influenced by interlayer coupling and band offsets, crucial for band-gap-engineered vertical heterostructures (VHs).
Purpose of the Study:
- To investigate the impact of interlayer coupling and band offset on SHG in 3R-type TMDC homobilayers and heterobilayers.
- To explore strategies for enhancing SHG efficiency in TMDC VHs for broadband applications.
Main Methods:
- Fabrication of 3R-type homobilayers and heterobilayers using MoS2 and MoS2(1-x)Sex alloys.
- Variation of interlayer coupling via SiO2 intercalation, dry transfer, and postannealing.
- Characterization using photoluminescence, Raman spectroscopy, reflectance difference spectroscopy, and atomic force microscopy.
Main Results:
- Interlayer coupling in MoS2 homobilayers induces band modifications, deviating SHG from the simple square law observed in decoupled layers.
- TMDC VHs broaden the spectral range for SHG but typically do not achieve coherent reinforcement due to phase differences.
- Postannealing of VHs in the overlapping resonance regime leads to unexpectedly high SHG enhancement.
Conclusions:
- Interlayer coupling is a critical factor controlling SHG in TMDC bilayers.
- Postannealing can create strong resonances in TMDC VHs, significantly boosting SHG efficiency.
- The developed approach shows promise for highly efficient broadband SHG applications using TMDC VHs.
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