Zhang Tianyi, Voshell Andrew, Zhou Da, Ward Zachary D, Yu Zhuohang, Liu Mingzu, Díaz Aponte Kevin O, Granzier-Nakajima Tomotaroh, Lei Yu, Liu He, Terrones Humberto, Elías Ana Laura, Rana Mukti, Terrones Mauricio
Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA.
Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA 16802, USA.
Nanoscale. 2023 Jul 27;15(29):12348-12357. doi: 10.1039/d3nr00961k.
The ultraflat and dangling bond-free features of two-dimensional (2D) transition metal dichalcogenides (TMDs) endow them with great potential to be integrated with arbitrary three-dimensional (3D) substrates, forming mixed-dimensional 2D/3D heterostructures. As examples, 2D/3D heterostructures based on monolayer TMDs (, WS) and bulk germanium (Ge) have become emerging candidates for optoelectronic applications, such as ultrasensitive photodetectors that are capable of detecting broadband light from the mid-infrared (IR) to visible range. Currently, the study of WS/Ge(100) heterostructures is in its infancy and it remains largely unexplored how sample preparation conditions and different substrates affect their photoluminescence (PL) and other optoelectronic properties. In this report, we investigated the PL quenching effect in monolayer WS/Ge heterostructures prepared a wet transfer process, and employed PL spectroscopy and atomic force microscopy (AFM) to demonstrate that post-transfer low-pressure annealing improves the interface quality and homogenizes the PL signal. We further studied and compared the temperature-dependent PL emissions of WS/Ge with those of as-grown WS and WS/graphene/Ge heterostructures. The results demonstrate that the integration of WS on Ge significantly quenches the PL intensity (from room temperature down to 80 K), and the PL quenching effect becomes even more prominent in WS/graphene/Ge heterostructures, which is likely due to synergistic PL quenching effects induced by graphene and Ge. Density functional theory (DFT) and Heyd-Scuseria-Ernzerhof (HSE) hybrid functional calculations show that the interaction of WS and Ge is stronger than in adjacent layers of bulk WS, thus changing the electronic band structure and making the direct band gap of monolayer WS less accessible. By understanding the impact of post-transfer annealing and substrate interactions on the optical properties of monolayer TMD/Ge heterostructures, this study contributes to the exploration of the processing-properties relationship and may guide the future design and fabrication of optoelectronic devices based on 2D/3D heterostructures of TMDs/Ge.
二维（2D）过渡金属二硫属化物（TMD）的超平坦且无悬空键的特性使其具有与任意三维（3D）衬底集成的巨大潜力，从而形成混合维度的2D/3D异质结构。例如，基于单层TMD（如WS）和块状锗（Ge）的2D/3D异质结构已成为光电子应用的新兴候选材料，如能够检测从中红外（IR）到可见光范围的宽带光的超灵敏光电探测器。目前，WS/Ge(100)异质结构的研究尚处于起步阶段，样品制备条件和不同衬底如何影响其光致发光（PL）及其他光电子特性在很大程度上仍未得到探索。在本报告中，我们研究了通过湿法转移工艺制备的单层WS/Ge异质结构中的PL猝灭效应，并采用PL光谱和原子力显微镜（AFM）来证明转移后低压退火可改善界面质量并使PL信号均匀化。我们进一步研究并比较了WS/Ge与生长态WS以及WS/石墨烯/Ge异质结构的温度相关PL发射。结果表明，WS在Ge上的集成显著猝灭了PL强度（从室温到80 K），并且在WS/石墨烯/Ge异质结构中PL猝灭效应变得更加显著，这可能是由于石墨烯和Ge诱导的协同PL猝灭效应所致。密度泛函理论（DFT）和Heyd-Scuseria-Ernzerhof（HSE）杂化泛函计算表明，WS与Ge的相互作用比块状WS相邻层中的相互作用更强，从而改变了电子能带结构并使单层WS的直接带隙更难达到。通过了解转移后退火和衬底相互作用对单层TMD/Ge异质结构光学特性的影响，本研究有助于探索加工-性能关系，并可能指导基于TMDs/Ge的2D/3D异质结构的光电器件的未来设计和制造。
