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      Room temperature near unity spin polarization in 2D Van der Waals heterostructures

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          Abstract

          The generation and manipulation of spin polarization at room temperature are essential for 2D van der Waals (vdW) materials-based spin-photonic and spintronic applications. However, most of the high degree polarization is achieved at cryogenic temperatures, where the spin-valley polarization lifetime is increased. Here, we report on room temperature high-spin polarization in 2D layers by reducing its carrier lifetime via the construction of vdW heterostructures. A near unity degree of polarization is observed in PbI 2 layers with the formation of type-I and type-II band aligned vdW heterostructures with monolayer WS 2 and WSe 2. We demonstrate that the spin polarization is related to the carrier lifetime and can be manipulated by the layer thickness, temperature, and excitation wavelength. We further elucidate the carrier dynamics and measure the polarization lifetime in these heterostructures. Our work provides a promising approach to achieve room temperature high-spin polarizations, which contribute to spin-photonics applications.

          Abstract

          In two-dimensional semiconductors, light can generate spin polarisations, however this effect is typically limited to low temperatures. By combining Lead Iodide (PbI 2) with transition metal dichalcogenides (TMDCs), the authors demonstrate room temperature light induced near-unity spin polarisations.

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          Two-dimensional material nanophotonics

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            Atomically thin p-n junctions with van der Waals heterointerfaces.

            Semiconductor p-n junctions are essential building blocks for electronic and optoelectronic devices. In conventional p-n junctions, regions depleted of free charge carriers form on either side of the junction, generating built-in potentials associated with uncompensated dopant atoms. Carrier transport across the junction occurs by diffusion and drift processes influenced by the spatial extent of this depletion region. With the advent of atomically thin van der Waals materials and their heterostructures, it is now possible to realize a p-n junction at the ultimate thickness limit. Van der Waals junctions composed of p- and n-type semiconductors--each just one unit cell thick--are predicted to exhibit completely different charge transport characteristics than bulk heterojunctions. Here, we report the characterization of the electronic and optoelectronic properties of atomically thin p-n heterojunctions fabricated using van der Waals assembly of transition-metal dichalcogenides. We observe gate-tunable diode-like current rectification and a photovoltaic response across the p-n interface. We find that the tunnelling-assisted interlayer recombination of the majority carriers is responsible for the tunability of the electronic and optoelectronic processes. Sandwiching an atomic p-n junction between graphene layers enhances the collection of the photoexcited carriers. The atomically scaled van der Waals p-n heterostructures presented here constitute the ultimate functional unit for nanoscale electronic and optoelectronic devices.
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              Electroluminescence and Photocurrent Generation from Atomically Sharp WSe2/MoS2 Heterojunction p–n Diodes

              The p–n diodes represent the most fundamental device building blocks for diverse optoelectronic functions, but are difficult to achieve in atomically thin transition metal dichalcogenides (TMDs) due to the challenges in selectively doping them into p- or n-type semiconductors. Here, we demonstrate that an atomically thin and sharp heterojunction p–n diode can be created by vertically stacking p-type monolayer tungsten diselenide (WSe2) and n-type few-layer molybdenum disulfide (MoS2). Electrical measurements of the vertically staked WSe2/MoS2 heterojunctions reveal excellent current rectification behavior with an ideality factor of 1.2. Photocurrent mapping shows rapid photoresponse over the entire overlapping region with a highest external quantum efficiency up to 12%. Electroluminescence studies show prominent band edge excitonic emission and strikingly enhanced hot-electron luminescence. A systematic investigation shows distinct layer-number dependent emission characteristics and reveals important insight about the origin of hot-electron luminescence and the nature of electron–orbital interaction in TMDs. We believe that these atomically thin heterojunction p–n diodes represent an interesting system for probing the fundamental electro-optical properties in TMDs and can open up a new pathway to novel optoelectronic devices such as atomically thin photodetectors, photovoltaics, as well as spin- and valley-polarized light emitting diodes, on-chip lasers.
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                Author and article information

                Contributors
                xiao_wang@hnu.edu.cn
                anlian.pan@hnu.edu.cn
                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group UK (London )
                2041-1723
                7 September 2020
                7 September 2020
                2020
                : 11
                : 4442
                Affiliations
                [1 ]GRID grid.67293.39, Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics, Hunan University, ; Changsha, 410082 China
                [2 ]GRID grid.67293.39, Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, College of Materials Science and Engineering, Hunan University, ; Changsha, 410082 China
                [3 ]GRID grid.411427.5, ISNI 0000 0001 0089 3695, Key Laboratory for Matter Microstructure and Function of Hunan Province, School of Physics and Electronics, Hunan Normal University, ; Changsha, 410081 China
                [4 ]GRID grid.10392.39, ISNI 0000 0001 2190 1447, Institute of Physical and Theoretical Chemistry and LISA+, University of Tübingen, ; Auf der Morgenstelle 18, 72076 Tübingen, Germany
                Author information
                http://orcid.org/0000-0002-2973-8215
                http://orcid.org/0000-0003-3335-3067
                Article
                18307
                10.1038/s41467-020-18307-w
                7477097
                32895376
                2302a166-f977-4f9b-81ed-c5531dc5f080
                © The Author(s) 2020

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 31 January 2020
                : 28 July 2020
                Funding
                Funded by: We acknowledge financial support from the National Natural Science Foundation of China (Nos. 91850116, 51772084, 51525202, 11774084 and 91833302), the Sino-German Center for Research Promotion (No. GZ1390), the Hunan Provincial Natural Science Foundation of China (No. 2018RS3051) and the Project of Educational Commission of Hunan Province of China (No. 18A003).
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                © The Author(s) 2020

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                nanoscience and technology,optics and photonics
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                nanoscience and technology, optics and photonics

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