RUI: Atomically thin monolayer semiconductors for ultrasensitive UV photodetectors

摘要：本研究主要研究由过渡金属二硫族化合物（TMDs）衍生的原子厚的二维半导体，其最终目标是为开发一种超灵敏、千兆赫兹速度的紫外（UV）光探测器奠定基础。目前，这种基于半导体的紫外光电探测器是不可用的，这阻碍了许多高速和低信号的应用。TMD半导体显示出非凡的特性。它们独特的晶体结构导致产生一种独特类型的强束缚激子，称为范霍夫奇点激子，当紫外光子与TMD半导体相互作用时产生。将研究TMD材料，以了解这些激子的基本物理性质，并将其用于紫外区域的光电应用，最终用于开发一种新的超快，快速响应和高灵敏度的紫外光电探测器。这项研究预计将对从日常生活到新的通信工具产生重大的技术影响。它将在一所主要的本科院校进行，参与者包括本科生、硕士生和当地高中的学生。积极参与该项目将为学生提供良好的纳米科学研究经验和纳米光电子学培训的绝佳机会，为他们在工业和学术界的职业生涯做好准备。首席研究员将在一年一度的湾区科学节上与当地社区接触，展示纳米技术的基本原理，激发公众对科学的兴趣，并鼓励年轻人攻读科学学位。摘要：新开发的原子级薄范德华晶体具有优异的电子、光学和光电学性能，为新型纳米级光电器件的开发提供了广阔的前景。该项目的目标是通过研究单层过渡金属二硫族化合物（TMDs）的有趣性质来推进对此类器件的基本理解。通过利用由MoS2， MoSe2， WS2和WSe2衍生的原子薄单层tmd中的van Hove奇点辅助激子跃迁，最终将开发出纳米级，超灵敏（~少数光子）和快速紫外光电探测器的原型。这些半导体独特的晶体结构创造了一个墨西哥帽状的光学带结构。状态的联合密度在墨西哥帽的底部发散，形成了范霍夫奇点。该项目的目标是：(i)通过测量光电流谱、光响应性和时间响应来研究由体晶衍生的单层TMDs的van Hove奇点辅助光电特性。（ii）研究大规模化学气相沉积tmd的固有光电性能，并测量其光电流和时间响应，以阐明线缺陷和晶界如何影响光电性能。(3)叠加单层tmd，开发具有高吸收、GHz光响应速度和少量光子探测能力的紫外光电探测器。这项研究将促进对物理学中新颖的多体激子现象的基本理解，不仅在二维系统中，而且在其他纳米尺度系统中，从玻色-爱因斯坦凝聚到激子太阳能电池，对可扩展纳米光子器件的发展有很大的希望。

Title: Atomically thin semiconductors for ultrasensitive UV PhotodetectorsNon-technical Abstract: This research focuses on atom-thick, two-dimensional semiconductors derived from transition metal dichalcogenides (TMDs) with the ultimate goal to lay the foundation for developing an ultrasensitive, gigahertz speed photodetector in the ultraviolet (UV) range. Currently, such a semiconductor-based UV photodetector is not available, which hampers many high speed and low signal applications. TMD semiconductors reveal remarkable properties. Their unique crystal structure leads to the creation of a unique type of strongly bound excitons, known as van Hove singularity excitons that are created when a UV photon interacts with a TMD semiconductor. TMD materials will be studied to understand the basic physical properties of these excitons and to utilize them for optoelectronic applications in the UV region and ultimately for the development of a new ultrafast, fast-response, and high-sensitivity UV photodetector. This research is expected to have significant technological impacts ranging from everyday life to new communication tools. It will be conducted at a Primarily Undergraduate Institution and will involve undergraduate and Master's students and students from local high schools. The active participation in the project will provide students an excellent nanoscience research experience and an outstanding opportunity to train in nanoscale optoelectronics preparing them for careers in industry and academia. The principal investigator will reach out to the local community at the Annual Bay Area Science Festival to showcase the underlying principles of nanotechnology seeding public interest in science and encouraging young adults to pursue science degrees.Technical-Abstract: Newly developed atomically thin van der Waals crystals reveal remarkable electronic, optical, and optoelectrical properties and show great promise for the development of novel nanoscale optoelectronic devices. The goal of the project is to advance the fundamental understanding of such devices by studying the intriguing properties of monolayer transition metal dichalcogenides (TMDs). Ultimately a prototype of a nanoscale, ultrasensitive (~few photons) and fast UV photodetector will be developed by exploiting van Hove singularity assisted excitonic transitions in atomically thin monolayer TMDs derived from MoS2, MoSe2, WS2 and WSe2. The unique crystal structures of these semiconductors create a Mexican hat-like optical band structure. The joint density of states diverges at the bottom of the Mexican hat creating the van Hove singularity. The objectives of the project are: (i) Investigate the van Hove singularity assisted optoelectronic properties of monolayer TMDs derived from bulk crystals by measuring the photocurrent spectra, photoresponsivity, and time responses. (ii) Investigate the intrinsic optoelectronic properties of large-scale chemical vapor deposited TMDs and measure their photocurrent and time responses to elucidate how line defects and grain boundaries affect the optoelectronic properties. (iii) Stack monolayer TMDs to develop a UV photodetector that exhibits high absorption, a GHz photoresponse speed, and a few photon detection ability. This research will advance the fundamental understanding of novel, many-body excitonic phenomena in physics, not only in 2D systems, but also in other nanoscale systems ranging from Bose-Einstein condensation to excitonic solar cells and has great promise for the development of scalable nanophotonic devices.