Exciton Manifolds in Highly Ambipolar Doped WS₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Physical Chemistry

Background:

• Studying single and many-particle properties in 2D semiconductors under high carrier concentrations is experimentally difficult using only optical methods.
• Understanding exciton binding and band gap energies in doped 2D materials is crucial for their technological applications.

Purpose of the Study:

• To establish a novel experimental platform for investigating exciton properties and band gap evolution in 2D semiconductors.
• To elucidate the origins of complex exciton manifolds and their doping dependencies in WS2 monolayers.

Main Methods:

• Fabrication of an electrolyte-gated WS2 monolayer field-effect device.
• Utilizing combined spectroscopic ellipsometry and photoluminescence spectroscopy.
• Performing measurements across a wide range of n- and p-type doping levels (up to 10^14 cm^-2).

Main Results:

• The device successfully tunes the Fermi level across the valence and conduction bands, enabling optical tracing of exciton binding and band gap energies.
• Two prominent photoluminescence emission bands were identified as originating from phonon-activated, spin- and momentum-forbidden excitonic recombination.
• Interband transitions were observed to be redshifted and weakened under both electron and hole doping.

Conclusions:

• The developed field-effect platform is effective for studying exciton manifolds in doped 2D materials.
• This platform facilitates combined optical and transport measurements on degenerately doped atomically thin quantum materials, even at cryogenic temperatures.