由石墨烯(Gr)和过渡金属二硫属化合物(TMD)组成的垂直范德华异质结构为探索二维极限中的光学和电子性质创造了一个迷人的平台。许多研究都集中在Gr/TMDs异质结构上,以阐明电荷能量转移的潜在机制。准粒子形成,和光学激发后的弛豫。然而,对基于石墨烯的异质结构中的界面电荷分离和后续动力学的全面理解仍然难以捉摸。这里,我们已经研究了Gr-MoS2异质结构(包括Gr/MoS2和MoS2/Gr堆叠序列)在不同的光激发能量下在熔融石英衬底上生长的载流子动力学。包括时间分辨太赫兹(THz)光谱,THz发射光谱,和瞬态吸收光谱学。我们的发现强调了衬底电场对调制界面电荷转移(CT)效率的影响。具体来说,例如,Gr/MoS2中的光学激发产生从石墨烯层到MoS2层中的热电子注入,其光子能量远低于MoS2的A-激子,而MoS2/Gr中的界面CT被衬底的电场阻挡。反过来,上述A激子的光激发导致空穴从MoS2转移到石墨烯,对于具有相反堆叠顺序的两个Gr-MoS2异质结构,导致界面光电流的相反方向,正如异相THz发射所直接证明的那样。此外,我们证明界面激子的复合时间约为〜18ps,而缺陷辅助界面复合发生在~ns的时间尺度上。这项研究为界面CT之间的相互作用提供了有价值的见解,底物效应,和Gr-TMD异质结构中的缺陷工程,从而促进下一代光电器件的发展。
Vertical van der Waals heterostructures composed of graphene (Gr) and transition metal dichalcogenides (
TMDs) have created a fascinating platform for exploring optical and electronic properties in the two-dimensional limit. Numerous studies have focused on Gr/
TMDs heterostructures to elucidate the underlying mechanisms of charge-energy transfer, quasiparticle formation, and relaxation following optical excitation. Nevertheless, a comprehensive understanding of interfacial charge separation and subsequent dynamics in graphene-based heterostructures remains elusive. Here, we have investigated the carrier dynamics of Gr-MoS2 heterostructures (including Gr/MoS2 and MoS2/Gr stacking sequences) grown on a fused silica substrate under varying photoexcitation energies by comprehensive ultrafast means, including time-resolved terahertz (THz) spectroscopy, THz emission spectroscopy, and transient absorption spectroscopy. Our findings highlight the impact of the substrate electric field on the efficiency of modulating the interfacial charge transfer (CT). Specifically, the optical excitation in Gr/MoS2 generates thermal electron injection from the graphene layer into the MoS2 layer with photon energy well below A-exciton of MoS2, whereas the interfacial CT in the MoS2/Gr is blocked by the electric field of the substrate. In turn, photoexcitation of the A exciton above leads to hole transfer from MoS2 to graphene, which occurs for both Gr-MoS2 heterostructures with opposite stacking orders, resulting in the opposite orientations of the interfacial photocurrent, as directly demonstrated by the out-of-phase THz emission. Moreover, we demonstrate that the recombination time of interfacial exciton is approximately ∼18 ps, whereas the defect-assisted interfacial recombination occurs on a time scale of ∼ns. This study provides valuable insights into the interplay between interfacial CT, substrate effects, and defect engineering in Gr-
TMDs heterostructures, thereby facilitating the development of next-generation optoelectronic devices.