Carrier and polarization dynamics in monolayer MoS2

Area of Science:

• Materials Science
• Condensed Matter Physics
• Optoelectronics

Background:

• Monolayer MoS2 exhibits chiral selection rules for optical transitions, enabling valley initialization.
• Optical properties of 2D materials are sensitive to temperature and excitation conditions.

Purpose of the Study:

• Investigate temperature-dependent optical polarization dynamics in monolayer MoS2.
• Determine the influence of excitation power and energy on photoluminescence polarization.
• Characterize exciton emission decay times and relaxation mechanisms.

Main Methods:

• Time-resolved photoluminescence (TRPL) spectroscopy.
• Variable temperature measurements (4 K to 300 K).
• Variable excitation power and photon energy studies.

Main Results:

• High photoluminescence (PL) polarization observed from 4 K to 300 K, independent of temperature within experimental resolution.
• PL polarization significantly decreases with increasing pulsed laser excitation power.
• Fast exciton emission decay time of approximately 4 ps.
• Initial polarization dominates steady-state PL, with no clear decay observed within ps resolution.
• Decreased initial polarization with increasing pump photon energy suggests possible ultrafast intervalley relaxation.
• Recovered 40% emission polarization at 300 K by compensating band gap energy changes.

Conclusions:

• Monolayer MoS2 exhibits robust optical polarization over a wide temperature range.
• Excitation power is a critical factor influencing PL polarization, potentially due to nonlinear effects or intervalley scattering.
• Ultrafast relaxation processes may occur beyond the ps timescale, influencing polarization.
• Temperature effects on band gap can be compensated to maintain high polarization, crucial for optoelectronic applications.