Threefold Symmetrical Growth of MoS₂ Homoepitaxial Patterns with Enhanced Valley Polarization

Hsiang-Chi Hu^1*, Tilo H. Yang¹, Yu-Fan Chiang¹, Ting-Hua Lu¹, Yann-Wen Lan¹

¹Department of physics, National Taiwan Normal University, Taipei, Taiwan

* Presenter:Hsiang-Chi Hu, email:hsiang890608@gmail.com

Monolayer transition-metal dichalcogenides (TMDCs) are promising semiconductor materials for opto-valleytronics and opto-spintronics thanks to their strong spin-valley coupling. In this regard, a reliable growth method to achieve controllable morphology of 2D TMDCs with high valley polarization is crucially important. Here, we report a detailed study on opto-valleytronic properties of fan-shaped bilayer MoS₂ grown by CVD. Such a fan-shaped MoS₂, with three-fold symmetrical structure, has yet to be reported and presents unique optical properties. By photoluminescence investigation, we found the A exciton peak from the bilayer domains shows blue shifting with respect to the monolayer, which is unusual compared with bilayer MoS₂ in previous studies. By illuminating Fan-shaped MoS₂ with circularly polarized light, the recorded circular polarization (P_circ) from the monolayer and the bilayer was about 20% and 40% at 297 K, respectively (P_circ ~80% for the bilayer at 77 K). The mechanism behind the high P_circ of the fan-shaped bilayer may be attributed to its 3R stacking configuration with weak interlayer coupling, which is associated with its unusual 3-fold symmetrical growth behavior.

Keywords: Transition-metal dichalcogenides, MoS₂, CVD, Valley Polarization, AFM