Biexciton Formation in Bilayer Tungsten Disulfide

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Monolayer transition metal dichalcogenides (TMDs) exhibit strong many-body effects due to large exciton binding energies.
• Bilayer TMDs present altered band structures, complicating the study of biexcitons.
• Understanding biexcitons in bilayer systems is crucial for advanced optoelectronics.

Purpose of the Study:

• Investigate biexciton emission in bilayer WS2.
• Determine the impact of strain and temperature on biexciton properties.
• Explore strain as a method to tune many-body effects in bilayer TMDs.

Main Methods:

• Chemical vapor deposition (CVD) for WS2 growth.
• Raman spectroscopy to quantify biaxial strain.
• Temperature-dependent photoluminescence spectroscopy to study biexciton emission.
• Density functional theory (DFT) calculations to model strain effects.

Main Results:

• Measured a biexciton binding energy of 36 ±4 meV in as-grown bilayer WS2 with 0.4% biaxial strain.
• Observed diminished biexciton emission upon strain release.
• DFT calculations confirmed strain's role in enhancing direct band gap transitions.
• Identified thermal dissociation of biexcitons with an activation energy of 26 ± 5 meV.

Conclusions:

• Strain significantly enhances biexciton emission in bilayer WS2 by tuning band structure.
• Strain engineering offers a pathway to control many-body effects in bilayer TMDs.
• These findings expand the potential of bilayer TMDs for photonic applications.