Polarity Tunable Trionic Electroluminescence in Monolayer WSe₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanoscience

Background:

• Monolayer transition metal dichalcogenides like WSe2 exhibit complex excitonic behavior due to strong many-body interactions.
• Exciton complexes, including trions (charged excitons), are crucial for understanding optical and electronic properties in 2D materials.

Purpose of the Study:

• To demonstrate selective electrical excitation of positive (X+) and negative (X-) trions in a WSe2-based heterostructure.
• To investigate the role of a van der Waals metal-insulator-semiconductor (MIS) heterostructure in controlling charge injection.
• To explore the potential for on-chip manipulation of excitonic properties in 2D semiconductors.

Main Methods:

• Fabrication of a van der Waals heterostructure comprising few-layer graphene (FLG), hexagonal boron nitride (hBN), and monolayer WSe2.
• Utilizing field-emission tunneling and electrostatic accumulation for unbalanced electron and hole injection.
• Applying bias conditions to achieve selective excitation and planar electroluminescence.

Main Results:

• Achieved selective electrical excitation of both positive (X+) and negative (X-) trions in the monolayer WSe2.
• Demonstrated that the hBN layer acts as a tunneling barrier, enabling controlled injection of electrons or holes from the FLG layer.
• Observed bias-dependent planar electroluminescence attributed to specific trion species.

Conclusions:

• The developed MIS heterostructure allows for precise electrical control over trion generation in WSe2.
• This work provides a pathway for manipulating hot carriers and excitonic states in 2D materials.
• The findings pave the way for developing novel on-chip excitonic devices utilizing 2D semiconductors.