Pin down the mechanism of Fermi-level pinning in metal/2D-semiconductor contacts

确定金属/二维半导体接触中费米能级钉扎的机制

• 批准号: 2004445
• 负责人: Zhixian Zhou
• 金额: $ 29.99万
• 依托单位: Wayne State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-07-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2004445&HistoricalAwards=false
• 关键词: Pin; down; mechanism; Fermi; level

Nontechnical Description: Atomically thin semiconductors, referred to as two-dimensional (2D) semiconductors, have recently emerged as potential candidate materials for next-generation low-power and high-performance electronics. 2D semiconductors’ atomic flatness, surface-smoothness and thickness-uniformity allow electronic devices, including transistors, to be made smaller and more densely-packed than is currently possible with silicon technology. Furthermore, the excellent mechanical strength and stretchability of 2D materials also open up new opportunities for next-generation flexible electronics. A critical component of transistors is the metal-semiconductor electrical contacts because charge carriers are injected and extracted through these contacts. In spite of the superb electronic and mechanical properties of 2D semiconductors, the performance of current prototype 2D-semiconductor-based electronic devices is still severely limited by the non-ideal metal-semiconductor contacts. Isolating and understanding which factors limit electrical contacts between metal-electrodes and 2D semiconductors remains a major materials challenge and prevents practical electronic application of 2D semiconductors. To address this knowledge gap, this research uses new methods to controllably modify and characterize the properties of 2D semiconductor interfaces with metals. This project tightly integrates research, education, and community outreach efforts through a series of activities such as summer research for high school students, coaching Science Olympiad teams and lab tours. The emphasis of the education component of this project is placed on promoting diversity through actively recruiting graduate and undergraduate students from underrepresented minority groups. Technical Description:Two-dimensional (2D) semiconductors with a suitable bandgap, a reasonably high mobility, excellent mechanical strength and high flexibility are promising channel materials for next generation flexible electronics beyond the scaling limit of silicon-based field-effect transistors. However, a major bottleneck in electronic applications of 2D semiconductors such as transition metal dichalcogenides is their tendency to form a substantial Schottky barrier with most metals at their contacts largely due to Fermi-level pinning effects. This is a strong disadvantage because low-resistance ohmic contacts are needed for realistic devices. The goal of this project is to establish a fundamental understanding of the Fermi-level pinning mechanism at metal/2D-semiconductor interfaces and subsequently develop comprehensive contact-engineering strategies to eliminate the Schottky barrier. This project uses 2D van der Waals contacts with negligible Fermi-level pinning as the baseline and controllably introduce various possible pinning factors to quantitatively understand their roles in Fermi-level pinning. A variety of materials characterization techniques such as photoelectron spectroscopy, atomic force microscopy and scanning tunneling microscopy/spectroscopy will be performed in conjunction with electrical transport measurements to correlate the materials properties with the Schottky barrier height. The knowledge gained from this study is expected to help design effective contact-engineering strategies to achieve ultralow-resistance ohmic contacts to 2D semiconductors, and open up new avenues for basic research on 2D electronic and optoelectronic materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术描述：原子薄半导体，称为二维 (2D) 半导体，最近已成为下一代低功耗和高性能电子器件原子平坦度、表面光滑度和厚度的潜在候选材料。均匀性使得包括晶体管在内的电子器件能够比目前的硅技术制造得更小、更密集。此外，二维材料优异的机械强度和可拉伸性也为电子器件带来了新的机遇。下一代柔性电子器件的关键组件是金属半导体电接触，因为电荷载流子是通过这些接触注入和提取的，尽管二维半导体具有出色的电子和机械性能，但当前原型二维半导体的性能。基于二维的电子器件仍然受到非理想金属半导体接触的严重限制，隔离和了解哪些因素限制金属电极和二维半导体之间的电接触仍然是一个主要的材料挑战。为了解决这一知识差距，本研究使用新方法来可控地修改和表征二维半导体与金属的界面特性，该项目通过一系列的研究、教育和社区推广工作紧密结合。高中生暑期研究、辅导科学奥林匹克团队和实验室参观等活动 该项目的教育部分重点是通过积极招募来自代表性不足的少数群体的研究生和本科生来促进多样性。具有合适带隙、相当高的迁移率、优异的机械强度和高灵活性的（2D）半导体是超越硅基场效应晶体管的尺寸限制的下一代柔性电子器件的有前途的沟道材料，然而，这是电子应用中的主要瓶颈。二维半导体（例如过渡金属二硫属化物）的一个缺点是，它们倾向于在接触处与大多数金属形成大量肖特基势垒，这主要是由于费米能级钉扎效应，这是一个很大的缺点，因为低电阻欧姆接触。该项目的目标是建立对金属/二维半导体界面的费米级钉扎机制的基本了解，并随后开发全面的接触工程策略以消除肖特基势垒。以可忽略不计的费米能级钉扎为基线，可控地引入各种可能的钉扎因子，以定量了解其在费米能级钉扎中的作用，例如光电子等多种材料表征技术。光谱学、原子力显微镜和扫描隧道显微镜/光谱学将与电传输测量结合起来，将材料特性与肖特基势垒高度相关联，预计从这项研究中获得的知识将有助于设计有效的接触工程策略，以实现超低势垒。 - 二维半导体电阻欧姆接触，为二维电子和光电材料基础研究开辟新途径。该奖项体现了 NSF 的法定使命，并已通过使用基金会的智力优点和更广泛的影响审查标准进行评估，认为值得支持。

项目成果

Accumulation-Type Ohmic van der Waals Contacts to Nearly Intrinsic WSe 2 Nanosheet-Based Channels: Implications for Field-Effect Transistors

与基于 WSe 2 纳米片的近本征通道的累积型欧姆范德华接触：对场效应晶体管的影响

• DOI: 10.1021/acsanm.1c01138
• 发表时间: 2021-05
• 期刊: ACS Applied Nano Materials
• 影响因子: 5.9
• 作者: Andrews, Kraig;Rijal, Upendra;Bowman, Arthur;Chuang, Hsun;Koehler, Michael R.;Yan, Jiaqiang;Mandrus, David G.;Chen, Pai;Zhou, Zhixian
• 通讯作者: Zhou, Zhixian

Ultrafast Photocurrent Response and High Detectivity in Two-Dimensional MoSe 2 -based Heterojunctions

二维 MoSe 2 异质结中的超快光电流响应和高探测率

• DOI: 10.1021/acsami.0c12155
• 发表时间: 2020-10
• 期刊: ACS Applied Materials & Interfaces
• 影响因子: 9.5
• 作者: Ornelas, Christian D.;Bowman, Arthur;Walmsley, Thayer S.;Wang, Tianjiao;Andrews, Kraig;Zhou, Zhixian;Xu, Ya
• 通讯作者: Xu, Ya

Low-Temperature 2D/2D Ohmic Contacts in WSe 2 Field-Effect Transistors as a Platform for the 2D Metal–Insulator Transition

WSe 2 场效应晶体管中的低温 2D/2D 欧姆接触作为 2D 金属绝缘体转变的平台

• DOI: 10.1021/acsami.0c21440
• 发表时间: 2021-02
• 期刊: ACS Applied Materials & Interfaces
• 影响因子: 9.5
• 作者: Stanley, Lily J.;Chuang, Hsun;Zhou, Zhixian;Koehler, Michael R.;Yan, Jiaqiang;Mandrus, David G.;Popović, Dragana
• 通讯作者: Popović, Dragana