Vertical van der Waals heterostructures have aroused great attention for their promising application in next-generation nanoelectronic and optoelectronic devices. The dielectric screening effect plays a key role in the properties of two-dimensional (2D) heterostructures. Here, we studied the dielectric screening effects on the excitonic properties and critical points (CPs) of the WS₂/MoS₂ heterostructure using spectroscopic ellipsometry (SE). Owing to the type-II band alignment of the WS₂/MoS₂ heterostructure, charged carriers spatially separated and created an interlayer exciton, and the transition energy and binding energy have been accurately found to be 1.58 ± 0.050 eV and 431.39 ± 127.818 meV by SE, respectively. We found that stacking the WS₂/MoS₂ vertical heterostructure increases the effective dielectric screening compared with the monolayer counterparts. The increased effective dielectric screening in the WS₂/MoS₂ heterostructure weakens the long-range Coulomb force between electrons and holes. Consequently, the quasi-particle band gap and the exciton binding energies are reduced, and because of the orbital overlap, more CPs are produced in the WS₂/MoS₂ heterostructure in the high photon energy range. Our results not only shed light on the interpretation of recent first-principles studies, but also provide important physical support for improving the performance of heterostructure-based optoelectronic devices with tunable functionalities.

中文翻译：

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介电筛选对WS2 / MoS2异质结构的激子和临界点性质的影响

垂直范德华异质结构因其在下一代纳米电子和光电器件中的应用前景而备受关注。介电屏蔽效应在二维（2D）异质结构的性质中起关键作用。在这里，我们使用光谱椭偏仪（SE）研究了介电屏蔽对WS ₂ / MoS ₂异质结构的激子性质和临界点（CP）的影响。由于WS ₂ / MoS ₂的II型频带对准异质结构，带电载流子在空间上分离并产生层间激子，并且通过SE准确地发现其跃迁能和结合能分别为1.58±0.050 eV和431.39±127.818 meV。我们发现，堆叠WS ₂ / MoS ₂垂直异质结构与单层对应结构相比增加了有效的介电筛选。WS ₂ / MoS ₂异质结构中有效介电屏蔽的增加削弱了电子与空穴之间的远程库仑力。因此，准粒子带隙和激子结合能降低，并且由于轨道重叠，WS ₂ / MoS ₂中产生了更多的CP。高光子能量范围内的异质结构。我们的结果不仅为最近的第一性原理研究提供了启示，而且为提高具有可调功能的基于异质结构的光电器件的性能提供了重要的物理支持。