Large Range Manipulation of Exciton Species in Monolayer WS2

TL;DR

This study demonstrates large-range manipulation of exciton and trion emissions in monolayer WS2 through photoexcitation power and temperature, revealing tunable excitonic ratios and insights into Coulomb interactions.

Contribution

It introduces a method to control exciton and trion populations in WS2 monolayers via photoexcitation and temperature, highlighting the effects of donor impurities and electron-phonon coupling.

Findings

Exciton-trion intensity ratio can be tuned from 0.1 to 7.7.

Resonance energies shift with temperature due to electron-phonon interactions.

Trion binding energy is approximately 23 meV and temperature-independent.

Abstract

Unconventional emissions from exciton and trion in monolayer WS2 are studied by photoexcitation. Excited by 532nm laser beam, the carrier species in the monolayer WS2 are affected by the excess electrons escaping from photoionization of donor impurity, the concentration of which varies with different locations of the sample. Simply increasing the excitation power at room temperature, the excess electron and thus the intensity ratio of excited trion and exciton can be continuously tuned over a large range from 0.1 to 7.7. Furthermore, this intensity ratio can also be manipulated by varying temperature. However, in this way the resonance energy of the exciton and trion show red-shifts with increasing temperature due to electron-phonon coupling. The binding energy of the trion is determined to be ~23meV and independent to temperature, indicating strong Coulomb interaction of carriers in such 2D materials.