Fu Shuai, du Fossé Indy, Jia Xiaoyu, Xu Jingyin, Yu Xiaoqing, Zhang Heng, Zheng Wenhao, Krasel Sven, Chen Zongping, Wang Zhiming M, Tielrooij Klaas-Jan, Bonn Mischa, Houtepen Arjan J, Wang Hai I
Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany.
Optoelectronic Materials Section, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, Netherlands.
Sci Adv. 2021 Feb 26;7(9). doi: 10.1126/sciadv.abd9061. Print 2021 Feb.
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-WS heterostructures by complementarily probing the ultrafast terahertz photoconductivity in graphene and the transient absorption dynamics in WS 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-WS interfaces, we find that it occurs via photo-thermionic emission for sub-A-exciton excitations and direct hole transfer from WS 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.
由石墨烯和过渡金属二硫属化物组成的范德华异质结构在光电子应用方面展现出了巨大潜力。然而，到目前为止，对器件运行的关键过程，即界面电荷转移（CT）和复合的深入理解仍然难以捉摸。在此，我们通过互补探测石墨烯中的超快太赫兹光电导率以及光激发后WS中的瞬态吸收动力学，来研究石墨烯-WS异质结构中的这些过程。我们观察到，电荷转移后异质结构中的分离电荷寿命极长：超过1纳秒，这与先前研究报道的约1皮秒的电荷分离情况形成对比。这导致了石墨烯的高效光控。此外，对于跨越石墨烯-WS界面的电荷转移过程，我们发现，对于亚A激子激发，它通过光热电子发射发生；对于高于A激子激发，它通过从WS到石墨烯价带的直接空穴转移发生。这些发现为进一步优化光电器件，特别是光电探测的性能提供了见解
