Spontaneous exciton dissociation in transition metal dichalcogenide monolayers.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 38295176.
- Also identified by DOI 10.1126/sciadv.adj4060 and PMC identifier 10830119.
- Licence recorded as CC BY-NC.
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Abstract
Since the seminal work on MoS<sub>2</sub>, photoexcitation in atomically thin transition metal dichalcogenides (TMDCs) has been assumed to result in excitons, with binding energies order of magnitude larger than thermal energy at room temperature. Here, we reexamine this foundational assumption and show that photoexcitation of TMDC monolayers can result in a substantial population of free charges. Performing ultrafast terahertz spectroscopy on large-area, single-crystal TMDC monolayers, we find that up to ~10% of excitons spontaneously dissociate into charge carriers with lifetimes exceeding 0.2 ns. Scanning tunneling microscopy reveals that photocarrier generation is intimately related to mid-gap defects, likely via trap-mediated Auger scattering. Only in state-of-the-art quality monolayers, with mid-gap trap densities as low as 10<sup>9</sup> cm<sup>-2</sup>, does intrinsic exciton physics start to dominate the terahertz response. Our findings reveal the necessity of knowing the defect density in understanding photophysics of TMDCs.