Wang Chen, Chen Yu, Suo Peng, Sun Kaiwen, Wang Shujie, Lin Xian, Liu Weimin, Ma Guohong
Department of Physics, Shanghai University, Shanghai 200444, China.
School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.
J Phys Chem Lett. 2025 Jun 26;16(25):6507-6512. doi: 10.1021/acs.jpclett.5c01633. Epub 2025 Jun 17.
The manipulation of interlayer and interfacial carrier transport in heterostructures represents a fundamental challenge in the design of next-generation optoelectronic devices. In this work, we employ ultrafast spectroscopy to investigate gate-tunable carrier dynamics in a prototypical van der Waals heterostructure: a vertically stacked molybdenum disulfide (MoS)/graphene (Gr) system. This material system has emerged as a promising platform for atomically thin optoelectronics due to its unique electronic properties. We fabricated a transparent field-effect transistor based on the Gr/MoS heterostructure and systematically studied the ultrafast charge transfer processes using complementary spectroscopic techniques: transient terahertz (THz) spectroscopy probes the photoconductivity dynamics in graphene, while transient absorption spectroscopy monitors the corresponding energy state evolution in MoS. Our findings demonstrate that both below- and above-bandgap excitations of the MoS layer yield gate-tunable THz photoconductivity responses in the heterostructure. Remarkably, we achieve picosecond-scale control over both the magnitude and sign (positive, negative, or zero) of the photoconductivity by modulating the graphene Fermi level and defect state occupation. This study provides fundamental insights into carrier dynamics in van der Waals heterostructures and establishes important design principles for developing advanced optoelectronic devices with tailored performance characteristics.
在异质结构中对层间和界面载流子传输进行调控，是下一代光电器件设计中的一项基本挑战。在这项工作中，我们采用超快光谱技术来研究一种典型范德华异质结构中的栅极可调载流子动力学：一种垂直堆叠的二硫化钼（MoS）/石墨烯（Gr）系统。由于其独特的电子特性，这种材料系统已成为用于原子级薄光电器件的一个有前景的平台。我们基于Gr/MoS异质结构制作了一个透明场效应晶体管，并使用互补光谱技术系统地研究了超快电荷转移过程：瞬态太赫兹（THz）光谱探测石墨烯中的光电导率动力学，而瞬态吸收光谱监测MoS中相应的能态演化。我们的研究结果表明，MoS层的带隙以下和带隙以上激发都会在异质结构中产生栅极可调的THz光电导率响应。值得注意的是，通过调制石墨烯费米能级和缺陷态占据情况，我们实现了对光电导率的大小和符号（正、负或零）的皮秒级控制。这项研究为范德华异质结构中的载流子动力学提供了基本见解，并为开发具有定制性能特征的先进光电器件确立了重要的设计原则。
