When graphene forms heterostructures with transition metal dichalcogenides (TMDCs), the photons with energy below the TMDCs’ bandgap can be harvested by graphene and injected into TMDCs through ultrafast charge transfer. Controlling and understanding this ultrafast charge transfer are crucial for developing advanced photonic and optoelectronic devices. Here, we use ultrafast terahertz and transient absorption spectroscopy to demonstrate the significant potential of a gate-controlled method in controlling the ultrafast charge transfer efficiency in graphene–MoS₂ heterostructures and reveal the fundamental limitation of the method. Our results show that the number of hot electrons transferred from graphene to MoS₂ can be modulated several fold by gate bias, achieved by altering the Fermi distribution of hot electrons in graphene. There is an upper limit to the gate-controlled method in the aforementioned modulation, and we reveal that the underlying mechanism of this limitation is that, at high gate bias, the chemical potential of graphene surpasses the band edge of MoS₂, leading to an increased energy barrier for charge transfer. A photothermionic emission model incorporating the gate-controlled limit can well reproduce the experimental findings. Our study demonstrates the role and fundamental limitation of the gate-controlled method in regulating ultrafast charge transfer in graphene–MoS₂ heterostructures, providing insights for the development of related photodetectors, solar cells, and optoelectronic devices.

中文翻译：

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揭示石墨烯-MoS2 异质结构中栅极控制超快电荷转移的基本极限


当石墨烯与过渡金属二硫化物 （TMDC） 形成异质结构时，能量低于 TMDC 带隙的光子可以被石墨烯收集并通过超快电荷转移注入 TMDC。控制和理解这种超快电荷转移对于开发先进的光子和光电器件至关重要。在这里，我们使用超快太赫兹和瞬态吸收光谱来证明门控方法在控制石墨烯-MoS₂ 异质结构中的超快电荷转移效率方面的巨大潜力，并揭示了该方法的基本局限性。我们的结果表明，通过改变石墨烯中热电子的费米分布，栅极偏压可以将从石墨烯转移到 MoS₂ 的热电子数量调制数倍。在上述调制中，栅极控制方法有一个上限，我们揭示了这个限制的潜在机制是，在高栅极偏压下，石墨烯的化学势超过了 MoS₂ 的带缘，导致电荷转移的能量势垒增加。包含门控极限的光热发射模型可以很好地再现实验结果。我们的研究证明了门控方法在调节石墨烯-MoS₂ 异质结构中超快电荷转移中的作用和基本局限性，为相关光电探测器、太阳能电池和光电器件的开发提供了见解。