Long-lived charge separation following pump-wavelength–dependent ultrafast charge transfer in graphene/WS2 heterostructures

Shuai Fu, Indy du Fossé, Xiaoyu Jia, Jingyin Xu, Xiaoqing Yu, Heng Zhang, Wenhao Zheng, Sven Krasel, Zongping Chen, Zhiming M. Wang, Klaas-Jan Tielrooij, Mischa Bonn (+2 others)
2021 Science Advances  
Van der Waals heterostructures consisting of graphene and transition metal dichalcogenides have shown great promise for optoelectronic applications. However, an in-depth understanding of the critical processes for device operation, namely, interfacial charge transfer (CT) and recombination, has so far remained elusive. Here, we investigate these processes in graphene-WS2 heterostructures by complementarily probing the ultrafast terahertz photoconductivity in graphene and the transient
more » ... transient absorption dynamics in WS2 following photoexcitation. We observe that separated charges in the heterostructure following CT live extremely long: beyond 1 ns, in contrast to ~1 ps charge separation reported in previous studies. This leads to efficient photogating of graphene. Furthermore, for the CT process across graphene-WS2 interfaces, we find that it occurs via photo-thermionic emission for sub-A-exciton excitations and direct hole transfer from WS2 to the valence band of graphene for above-A-exciton excitations. These findings provide insights to further optimize the performance of optoelectronic devices, in particular photodetection.
doi:10.1126/sciadv.abd9061 pmid:33637529 fatcat:f77ru3ldlnhd5a3abjmh3vnw2e