Wang Chao, Xu Wen, Mei Hongying, Qin Hua, Zhao Xinnian, Zhang Chao, Yuan Haifeng, Zhang Jin, Xu Yong, Li Peng, Li Ming
Opt Lett. 2019 Sep 1;44(17):4139-4142. doi: 10.1364/OL.44.004139.
We study terahertz (THz) optoelectronic properties of monolayer (ML) MoS placed on different substrates such as SiO/Si, sapphire, and quartz. Through the measurements of THz Fourier transform spectroscopy (2.5-6.5 THz) and THz time-domain spectroscopy (TDS, 0.2-1.2 THz), we find that the real part of optical conductivity increases for ML MoS on SiO/Si and sapphire substrates and decreases for it on quartz with increasing radiation frequency. It is shown that the complex optical conductivity for ML MoS, obtained from THz TDS measurements, can fit very well to the Drude-Smith formula. Thus, the dependence of optical conductivity of ML MoS on different substrates can be understood via a mechanism of electronic localization, and the electron density, relaxation time, and localization factor of the sample can be determined optically. Furthermore, we examine the influence of temperature on these key parameters in ML MoS on different substrates. The results obtained from this Letter indicate that THz spectroscopy is a very powerful tool in studying and characterizing ML MoS-based electronic systems, especially in examining the electronic localization effect which cannot be directly measured in conventional electrical transport experiment. This Letter is relevant to an in-depth understanding of the optoelectronic properties of ML MoS and of the proximity effect induced by different substrates.
我们研究了置于不同衬底（如SiO/Si、蓝宝石和石英）上的单层（ML）MoS的太赫兹（THz）光电特性。通过太赫兹傅里叶变换光谱（2.5 - 6.5 THz）和太赫兹时域光谱（TDS，0.2 - 1.2 THz）测量，我们发现随着辐射频率增加，置于SiO/Si和蓝宝石衬底上的ML MoS的光导率实部增加，而置于石英上的ML MoS的光导率实部减小。结果表明，通过太赫兹TDS测量得到的ML MoS的复光导率能很好地拟合德鲁德 - 史密斯公式。因此，ML MoS在不同衬底上的光导率依赖性可通过电子局域化机制来理解，并且样品的电子密度、弛豫时间和局域化因子可通过光学方法确定。此外，我们研究了温度对置于不同衬底上的ML MoS中这些关键参数的影响。从本信函中获得的结果表明，太赫兹光谱是研究和表征基于ML MoS的电子系统的非常强大的工具，特别是在研究传统电输运实验中无法直接测量的电子局域化效应方面。本信函有助于深入理解ML MoS的光电特性以及不同衬底引起的近邻效应。
