Nonlinear optical effect of interlayer charge transfer in a van der Waals heterostructure
Nonlinear optical effect of interlayer charge transfer in a van der Waals heterostructure
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DOI：
10.1063/1.5131165
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发表时间：
2019-12
影响因子：
4
通讯作者：
Peng Yao;D. He;Peymon Zereshki;Yongsheng Wang;Hui Zhao
中科院分区：
文献类型：
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作者：
Peng Yao;D. He;Peymon Zereshki;Yongsheng Wang;Hui Zhao
最近发现的二维材料可以用来制作多层异质结构。层间电荷转移是这种异质结构中的一个关键过程，因为它可以使出现的光电性能。在测量层间载流子分布的基础上，通过飞秒瞬态吸收光谱和稳态光谱测量，观察到了货车德瓦耳斯异质结构中有效的层间电荷转移.在这里，我们表明，二次谐波产生过程允许直接探测由电荷转移引起的电场。利用超短激光脉冲在MoS 2/WS 2异质结中激发电子和空穴。电子和空穴从两个单层的分离产生电场，这使得能够产生入射基波脉冲的二次谐波。我们进一步研究了该电场的时间演化，通过测量作为泵和基本脉冲之间的时间延迟的函数的二次谐波信号。结果与瞬态吸收测量所揭示的动态一致。这些结果提供了层间电荷转移的直接证据，并展示了研究二维材料中电荷转移和感生电场的全光学方法。此外，这种效应，如果足够大，可以利用在光学器件的基础上的二维异质结构与非线性光学响应的层间电荷转移可控。
The recently discovered two-dimensional materials can be used to fabricate multilayer heterostructures. Interlayer charge transfer is a key process in such heterostructures as it can enable emergent optoelectronic properties. Efficient interlayer charge transfer in van der Waals heterostructures has been observed by femtosecond transient absorption and steady-state optical spectroscopy measurements, based on measuring the interlayer carrier distribution. Here, we show that a second harmonic generation process allows direct probing of the electric field induced by the charge transfer. An ultrashort laser pulse was used to excite electrons and holes in a MoS2/WS2 heterostructure. The separation of the electrons and holes from the two monolayers generates an electric field, which enables the generation of the second harmonic of an incident fundamental pulse. We further studied the time evolution of this electric field by measuring the second harmonic signal as a function of the time delay between the pump and the fundamental pulses. The result agrees well with the dynamics revealed by a transient absorption measurement. These results provide direct evidence of interlayer charge transfer and demonstrate an all-optical method of studying charge transfer and induced electric fields in two-dimensional materials. Furthermore, this effect, if large enough, could be utilized in optical devices based on 2D heterostructures with nonlinear optical responses controllable by interlayer charge transfer.