Spontaneous Exciton Dissociation in Transition Metal Dichalcogenide Monolayers
| Autor: | Handa, Taketo, Holbrook, Madisen A., Olsen, Nicholas, Holtzman, Luke N., Huber, Lucas, Wang, Hai I., Bonn, Mischa, Barmak, Katayun, Hone, James C., Pasupathy, Abhay N., Zhu, X. -Y. |
|---|---|
| Rok vydání: | 2023 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| Popis: | Since the seminal work on MoS2 monolayers, photoexcitation in atomically-thin transition metal dichalcogenides (TMDCs) has been assumed to result in excitons with large binding energies (~ 200-600 meV). Because the exciton binding energies are order-of-magnitude larger than thermal energy at room temperature, it is puzzling that photocurrent and photovoltage generation have been observed in TMDC-based devices, even in monolayers with applied electric fields far below the threshold for exciton dissociation. Here, we show that the photoexcitation of TMDC monolayers results in a substantial population of free charges. Performing ultrafast terahertz (THz) spectroscopy on large-area, single crystal WS2, WSe2, and MoSe2 monolayers, we find that ~10% of excitons spontaneously dissociate into charge carriers with lifetimes exceeding 0.2 ns. Scanning tunnelling microscopy reveals that photo-carrier generation is intimately related to mid-gap defect states, likely via trap-mediated Auger scattering. Only in state-of-the-art quality monolayers14, with mid-gap trap densities as low as 10^9 cm^-2, does intrinsic exciton physics start to dominate the THz response. Our findings reveal that excitons or excitonic complexes are only the predominant quasiparticles in photo-excited TMDC monolayers at the limit of sufficiently low defect densities. Comment: 18 pages, 5 figures, SI |
| Databáze: | arXiv |
| Externí odkaz: |
|