Department of Physics, Washington University in St. Louis , St. Louis, Missouri 63136, United States.
Institute of Materials Science and Engineering, Washington University in St. Louis , St. Louis, Missouri 63136, United States.
Nano Lett. 2017 Dec 13;17(12):7809-7813. doi: 10.1021/acs.nanolett.7b04021. Epub 2017 Nov 30.
Bilayer van der Waals (vdW) heterostructures such as MoS/WS and MoSe/WSe have attracted much attention recently, particularly because of their type II band alignments and the formation of interlayer exciton as the lowest-energy excitonic state. In this work, we calculate the electronic and optical properties of such heterostructures with the first-principles GW+Bethe-Salpeter Equation (BSE) method and reveal the important role of interlayer coupling in deciding the excited-state properties, including the band alignment and excitonic properties. Our calculation shows that due to the interlayer coupling, the low energy excitons can be widely tuned by a vertical gate field. In particular, the dipole oscillator strength and radiative lifetime of the lowest energy exciton in these bilayer heterostructures is varied by over an order of magnitude within a practical external gate field. We also build a simple model that captures the essential physics behind this tunability and allows the extension of the ab initio results to a large range of electric fields. Our work clarifies the physical picture of interlayer excitons in bilayer vdW heterostructures and predicts a wide range of gate-tunable excited-state properties of 2D optoelectronic devices.
双层范德华（vdW）异质结构，如 MoS/WS 和 MoSe/WSe，最近引起了广泛关注，特别是由于它们的 II 型能带排列以及层间激子的形成作为最低能量激子态。在这项工作中，我们使用第一性原理 GW+Bethe-Salpeter 方程（BSE）方法计算了这种异质结构的电子和光学性质，并揭示了层间耦合在决定激发态性质中的重要作用，包括能带排列和激子性质。我们的计算表明，由于层间耦合，垂直栅极场可以广泛调节低能量激子。特别是，在这些双层异质结构中，最低能量激子的电偶极振子强度和辐射寿命在实际的外部栅极场中可以变化一个数量级以上。我们还建立了一个简单的模型，该模型捕捉了这种可调谐性背后的基本物理原理，并允许将从头算结果扩展到很大的电场范围。我们的工作阐明了双层 vdW 异质结构中层间激子的物理图像，并预测了二维光电设备的大范围栅极可调激发态性质。
