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Distinct Valley Polarization in Vertical Heterobilayers: Difference between Edge- and Center-Nucleated WS2/MoS2
Chinh Tam Le1, Je-Ho Lee2, Nguyen The Hoang2
1Department of Semiconductor Physics & Engineering and Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 44610, South Korea.
ACS Applied Materials & Interfaces
|July 17, 2024
Summary
Structural defects impact transition metal dichalcogenides (TMDs) excitonic properties. Defect healing in center-nucleated TMD vertical heterobilayers (VHs) restores valley polarization, crucial for valleytronic devices.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Nanotechnology
Background:
- Structural imperfections in transition metal dichalcogenides (TMDs) influence excitonic properties.
- Defects typically cause valley depolarization in monolayer TMDs, but can be healed in vertical heterobilayers (VHs).
Purpose of the Study:
- To analyze valley polarization in center-nucleated and edge-nucleated VHs (WS2/MoS2).
- To investigate the impact of defect healing and density on valley polarization.
- To explore temperature and excitation intensity dependence of valley depolarization.
Main Methods:
- Controlled growth process for WS2/MoS2 VHs.
- Photoluminescence (PL) spectroscopy to analyze valley polarization.
- Temperature-dependent and excitation intensity-dependent PL studies.
Main Results:
- Defect-related PL is suppressed in center-nucleated VHs due to defect healing.
- Lower-lying intralayer excitons are more sensitive to defect density than higher-lying ones.
- Valley depolarization of lower-lying excitons increases below 100 K due to defect state hybridization.
- Electron-doping-induced Auger recombination contributes to valley depolarization.
Conclusions:
- Defect healing is effective in center-nucleated TMD VHs.
- Valley polarization in TMD VHs is sensitive to defect density and temperature.
- Understanding these mechanisms is vital for developing VH-based valleytronic devices.
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