基于二硫化钼的新型半导体器件中无序效应对载流子输运的影响的研究

Two dimensional material based semiconductor devices are inducing more and more research interests since its inherited excellent gate control ability as the electrical devices scale down to nano-meter regime. Among the founded two dimensional materials, single layer MoS2 are standing out because of its 1.8 eV direct band gap and moderate carrier mobility. Single layer MoS2 is thought to have great potential for the application of electrical devices, and is promising materials to make electrical devices scaling trend continuing. The electrical devices based on single layer MoS2 have exhibited very good performance in experiment. Both the experimental and theoretical researches on MoS2 are in its infant stage. The mobility measured in the experiments are scattered in a wide range, while no commonly accepted theory can explain all the experimental results. In addition, the theoretical researches on disorder effects, such as line edge roughness and the effect of substrates and gate dielectric materials on carrier transport, are missing. In this project, the carrier transport behaviors in MoS2 based devices will be investigated comprehensively by modeling and simulation approach in theory. The first principle calculation method will be employed to calculate effects that dominate carrier transport such as electronic structure, phonon dispersion and the strength of electron-phonon coupling with the presence of disorder effect. With these above calculated results, transport models in which disorder effect such as line edge roughness, the effect of substrates and gate dielectric materials on carrier transport is considered can be proposed. Based on these models, the simulator which can simulate carrier transport behavior in MoS2 based electrical devices by numerical method will be developed. The developed numerical simulators can give the evaluation of carrier mobility in MoS2 based electrical devices with influences of different disorder situations. This project can help us to enrich the understanding of the carrier transport mechanisms in MoS2 based electrical devices, and provide theory and models for the further development and optimization of MoS2 based electrical devices. This project will also deepen our knowledge about carrier transport in low dimensional systems.

随着器件尺寸的不断缩小，基于二维材料的半导体器件由于其天然的优越栅控能力，正逐步成为研究的热点。基于新近发现的单层MoS2材料制备的电子器件展示了优越的性能和实用的潜力。实验上测量得到的MoS2的迁移率数值离散范围极大，理论计算不能完全解释此实验现象。同时理论上缺少对界面边缘粗糙、衬底或栅介质等无序效应对载流子输运的影响的研究。本项目将深入研究单层MoS2中载流子（电子和空穴）的输运行为，对单层MoS2的电子结构、声子色散关系、电声耦合强度等影响载流子输运的关键因素进行研究，发展计入多种无序效应的MoS2器件的载流子输运模型，利用上述模型对MoS2器件的载流子输运行为进行理论模拟研究和相关物理机制分析，评估无序效应影响下的载流子迁移率，加深我们对MoS2器件中的载流子输运机理的理解，为MoS2半导体器件的发展和优化设计提供理论基础和实用模型,解决低维系统输运的共性问题。

随着2004年石墨烯二维材料被发现，2010年发现石墨烯的两位科学家被授予诺贝尔物理学奖，二维材料一直是新型电子材料的研究热点。单层硫化钼作为一种新近发现的二维材料，由于其具有1.8 eV的本征带隙，相比于石墨烯，更适合用于电子器件。. 在过去三年中，围绕着外界无序效应对基于单层二硫化钼的新型半导体器件中的载流子迁移率的影响，本课题组开展了相关研究，取得的主要成果如下：. (1) 使用蒙特卡洛方法，对单层硫化钼中的声子散射对迁移率的影响进行了研究。研究表明，光学波声子散射是单层硫化钼迁移率高场退化的主要因素。. (2) 针对目前实验中关于硫化钼迁移率存在的争论，我们通过研究MOS结构中的高K栅介质对单层硫化钼的影响，明确指出是由于高K栅介质中的远程声子的作用，导致了霍尔测量实验中的载流子迁移率比理论计算值低一个数量级。同时，我们还提出了如何减弱高K栅介质中的远程声子作用的新型结构。. (3) 我们使用第一性原理方法，对单轴和双轴拉应力和压应力对单层硫化钼的电子结构的影响进行了研究。研究表明，压应力会导致单层二硫化钼从直接禁带变成间接禁带，带隙减小。拉应力对单层二硫化钼价带顶的影响较小。拉应力会增大单层二硫化钼的电子有效质量，压应力会减小单层二硫化钼的电子有效质量。. (4) 我们开发了适用于单层二硫化钼的非平衡格林函数量子输运模拟程序。模拟结果表明，对于5纳米超短沟道单层二硫化钼晶体管来说，拉应力导致的较小电子有效质量反而导致了较差的晶体管性能，这和我们通常认为的小电子有效质量有利于提升晶体管性能相违背。. (5) 本课题组对金属源漏对单层二硫化钼晶体管性能的影响进行了研究，提出了金属源漏单层二硫化钼晶体管的性能优化设计方法，对未来的单层二硫化钼晶体管的设计具有一定的指导作用。. 在该项目的资助下，已正式发表期刊论文9篇，会议论文5篇，投稿期刊论文2篇。