Theoretical and experimental study of optical properties of 2D material heterostructures

随着光基技术在现代世界中不可或缺，对高性能新型光学材料的需求不断增长，光学器件在能效和成本效益方面的优化受到越来越多的关注。低维材料具有比大块材料更独特的优势，有望实现下一代创新技术。特别是，垂直堆叠二维材料为异质结构和带隙工程提供了巨大的可能性。本文将对MoSe2/MoTe2和WSe2/MoTe2单层（ML）异质结构（HS）的光学性质进行理论和实验的联合研究。通过这种方式，通过研究MoSe2/MoTe2的ii型HS是否/如何保持其相应MLs的直接带隙，以及由于层间（或间接）激子的存在而成为光伏器件和探测器的有希望的候选者，将证明对这类材料及其可能应用的理解；- WSe2/MoTe2的i型HS由于存在层内（或直接）激子，是应用于低阈值二极管激光器的理想结构；-异质结构使MLs的光学性能恶化；-晶格失配和衬底对HS的光学性能有显著影响。

As light-based technologies have become indispensable in our modern world, demand for high-performing novel optical materials is growing and optimization of optical devices with respect to energy efficiency and cost effectiveness receives much attention. Low-dimensional materials feature unique advantages over their bulk counterparts and are expected to enable next-generation innovative technologies. Particularly, the opportunity of vertically stacking 2D materials offers vast possibilities of heterostructuring and band-gap engineering. Here, a joint theoretical and experimental study of optical properties of the (yet unexplored) MoSe2/MoTe2 and WSe2/MoTe2 monolayer (ML) heterostructures (HS) will be conducted. In this way the understanding of this material class and their possible applications will be demonstrated by investigating whether/how- Type-II HS of MoSe2/MoTe2 retains the direct band gap of their corresponding MLs and is a promising candidate for photovoltaic devices and detectors due to the presence of interlayer (or indirect) excitons;- Type-I HS of WSe2/MoTe2 is an ideal structure to be applied in low-threshold diode lasers due to the presence of intralayer (or direct) excitons;- Heterostructuring deteriorates the optical properties of MLs;- Lattice mismatch and substrate significantly affect the optical properties of HS.