Pt薄膜衬底H堆叠WS₂/WSe₂层间激子的谷极化研究

Valley Polarization of Interlayer Excitons in a H-stacked WS₂/WSe₂ on Pt Film Substrate

摘要

双层莫尔过渡金属硫族化合物（Transition metal dichalcogenides, TMDCs）可形成周期性的莫尔超晶格，是研究电子关联态和新型激子态的重要研究平台。具有II型能带匹配的转角TMDCs异质结形成的莫尔层间激子，其自旋-能谷自由度不仅能被静电感应、应力、衬底等因素调控，更受到莫尔势的深度调制，共同促进了高度可调谷电子学器件的研究。本文制备了分别位于铂（Pt）薄膜衬底和二氧化硅（SiO₂）衬底的H堆叠（60°转角）二硫化钨/二硒化钨（WS₂/WSe₂）异质结器件。通过低温下对两种衬底的莫尔异质结进行光致发光（Photoluminescence,PL）光谱、光致发光激发（Photoluminescence excitation,PLE）光谱以及谷极化的测试，发现在电荷掺杂可以忽略的情况下，层间激子在Pt衬底上更加局域化，并且其谷极化随激子浓度增加更容易饱和。本项工作中，Pt薄膜作为金属接触的同时也是一种人工引入的缺陷，其对异质结谷极化的影响为以莫尔层间激子为基础的光电子学应用提供了参考。

Abstract

Two-dimensional transition metal dichalcogenides (TMDCs) can form periodic moiré superlattice, offering an invaluable platform for the investigation of electron correlation states and novel exciton states. Moiré interlayer excitons in TMDCs heterostructures with type-II band alignment exhibit spin-valley degrees of freedom that are manipulated not only by electrostatic field, strain, and substrate, but also by the modulation of moiré potential, facilitating the exploration of highly tunable valleytronic devices. In this paper, a H-stacked (60° twisted) tungsten disulfide/tungsten diselenide (WS₂/WSe₂) heterostructure was prepared on platinum (Pt) thin film substrate and silicon dioxide (SiO₂) substrate, separately. By performing photoluminescence (PL) spectroscopy, photoluminescence excitation (PLE) spectroscopy and valley polarization measurements on both substrates at low temperatures, it was observed that, in the absence of significant charge doping, the interlayer excitons are more localized on the Pt substrate. Additionally, the valley polarization is more easily saturated with increasing exciton concentration on Pt substrate. Pt thin films, serving dual roles as metal contacts and artificially introduced defects, are shown to impact the valley polarization of the interlayer excitons. Our work provides insights for optoelectronics applications based on Moiré interlayer excitons.

Graphical abstract

关键词

H堆叠WS₂/WSe₂ / 层间激子 / 光致发光光谱 / 谷极化

Key words

H-stacked WS₂/WSe₂ / interlayer excitons / photoluminescence spectroscopy / valley polarization

基金资助

国家自然科学基金(12204287)