Free Trions with Near-Unity Quantum Yield in Monolayer MoSe₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Optoelectronics

Background:

• Trions are quasiparticles with potential in optoelectronics, exhibiting unique valley/spin properties in transition metal dichalcogenide (TMD) semiconductors.
• Previous research on trions in TMDs was limited by low materials quality, resulting in poor photoluminescence quantum yield (PL QY) and short lifetimes.
• High defect densities in TMDs have obscured the intrinsic properties and device potential of trions.

Purpose of the Study:

• To investigate the impact of atomic defect density on trion behavior in molybdenum diselenide (MoSe2) monolayers.
• To determine the relationship between material quality and trion photoluminescence quantum yield (PL QY) and lifetime.
• To enable the study of intrinsic trion properties and their diffusion dynamics.

Main Methods:

• Fabrication and characterization of a series of MoSe2 monolayer samples with defect densities varying over two orders of magnitude.
• Measurement of photoluminescence (PL) quantum yield (QY) as a function of defect density.
• Simultaneous measurement of PL lifetime to extract radiative and nonradiative components.

Main Results:

• Trion PL QY increases significantly with decreasing defect density, approaching unity in the highest quality MoSe2 monolayers.
• PL lifetime measurements reveal both intrinsic radiative and defect-dependent nonradiative lifetimes.
• A long trion lifetime of approximately 230 ps was observed, enabling direct observation of trion diffusion.

Conclusions:

• Achieving high material quality is crucial for maximizing trion PL QY and lifetime in MoSe2 monolayers.
• The long observed trion lifetime in high-quality materials opens possibilities for studying their diffusion and utilizing them in optoelectronic devices.
• Defect density is a key parameter controlling trion properties and performance in TMD semiconductors.