Gustafson, Jon K.Cunningham, Paul D.McCreary, Kathleen M.Jonker, Berend T.Hayden, L. Michael2020-01-302020-01-302019-11-19Gustafson, Jon K.; Cunningham, Paul D.; McCreary, Kathleen M.; Jonker, Berend T.; Hayden, L. Michael; Ultrafast Carrier Dynamics of Monolayer WS2 via Broad-Band Time-Resolved Terahertz Spectroscopy; The Journal of Physical Chemistry 123, 50, 30676-30683 (2019); https://pubs.acs.org/doi/10.1021/acs.jpcc.9b08483http://hdl.handle.net/11603/17194We report on the ultrafast carrier dynamics of monolayer WS2 using broad-band time-resolved terahertz spectroscopy (TRTS). We find that upon photoexcitation, there is an increase in the conductivity. We attribute this photoinduced increase in conductivity to ultrafast positive trion formation. Trion formation in two-dimensional materials is a consequence of the enhanced Coulombic interactions between electrons and holes. We find that trions in monolayer WS2 contribute to the photoconductivity in three ways: a Drude response, a broad resonance response, and a dissociation response at the trion binding energy. This is the first direct measurement of the trion binding energy in the far-infrared. Our results provide a comprehensive understanding of how trions behave in two-dimensional systems and should be broadly useful in studying the carrier dynamics of other two-dimensional systems.8 pagesen-USThis item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.Public Domain Mark 1.0This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.excitonsphotonicsabsorptionmonolayerselectrical conductivityText