二维单层NbxW1-xS2两步法制备及其场效应晶体管界面调控研究

The studies of high performance p-FET have been an urgent requirement for the further development of microelectronics technology. However, these key problems in the study of p-FET need to be solved urgently such as poor drive performance of the device, and low mobility of channel material, et al. This project develops a novel p-type two-dimensional monolayer NbxW1-xS2 with high mobility and good stability by introduing Nb in WS2 film using two-step process. Preparation of new p-FETs with the channel based on monolayer NbxW1-xS2 and high-k gate dielectric based on SrHfON film. New idea has been proposed to decrease the contact resistance of NbxW1-xS2/Pd and to improve the drive performance of the device by introducing vacancies in monolayer NbxW1-xS2. This project will study the two-step processes, micro-structure and physical properties of monolayer NbxW1-xS2, and investigate the regulatory law of vacancy defect on interfacial micro-structure and the electrical properties of the p-FET. Theoretical calculations and experiments are verified mutually to reveal effects of Nb doping on the p-type conductivity properties of the two-dimensional monolayer NbxW1-xS2, to clarify the interfacial defect regulatory mechanism of NbxW1-xS2/Pd heterojunction, and to obtain influnce rule and mechanism of multiple interfaces coupling on drive performance of p-FET device. This project will provide the innovative research ideas on further improving the drive performance of p-FET, and present substantial experimental and scientific basis for further enriching defect regulatory theory of FET.

高性能p型场效应晶体管（p-FET）的研究是微电子技术发展的迫切要求。目前，p-FET面临沟道迁移率低、驱动性能差等关键问题亟待解决。本项目提出采用两步法在二维WS2中掺入 Nb，创新性地制备一种高迁移率的p型导电二维单层NbxW1-xS2。再以单层NbxW1-xS2为沟道、以SrHfON为栅介质制备新型p-FET，并提出引入空位缺陷降低NbxW1-xS2/Pd界面接触电阻、提高器件驱动性能的新思路。研究单层NbxW1-xS2的两步法制备、微结构及物理特性，分析p-FET各界面微结构及界面的缺陷调控规律。理论计算和实验相互验证，揭示二维单层NbxW1-xS2的p型导电特性变化规律和影响机理，阐明NbxW1-xS2/Pd界面电学性质的缺陷调控机制，获得多元界面耦合作用对p-FET器件驱动性能的影响规律及影响机理。为进一步提高p-FET驱动性能和丰富FET界面调控理论提供充实的实验和科学依据。

针对p型二维场效应晶体管（FET）研究中面临的驱动性能低、稳定性差等问题，本项目提出开发一种高迁移率、稳定的p型二维NbxW1-xS2及其FET。采用物理气相输运及原位硫化两步法制备二维NbxW1-xS2，系统研究了制备工艺对二维NbxW1-xS2生长规律的影响，获得了二维NbxW1-xS2两步法可控制备工艺。成功制备出厚度为1~5 nm，平均尺寸为150 μm的单层和多层二维NbxW1-xS2。研究表明，该方法制备的二维WS2和二维NbxW1-xS2均呈现六方单晶特性，且制备出的二维NbxW1-xS2薄膜纯度高，不含其他杂质元素。理论计算与实验测试相结合，揭示了Nb掺杂对二维NbxW1-xS2、电极/NbxW1-xS2界面和NbxW1-xS2 FET性能的影响规律。研究表明，Nb掺杂WS2呈现p型导电。随着Nb掺杂浓度的增加，空穴有效质量降低，有利于空穴导电，且电极/NbxW1-xS2界面的隧道输运效率提高。但是，Nb掺杂浓度增加会导致二维NbxW1-xS2的形成能增大，稳定性变差。二维WS2 FET为n型，器件的迁移率较低。Nb掺杂后，二维NbxW1-xS2 FET为p型，且器件的迁移率表现出先增大后减小的趋势。在Nb掺杂量较低时，电极/NbxW1-xS2界面间电荷密度增大、界面电荷转移增加，电极/NbxW1-xS2界面的隧道势垒和肖特基势垒都相应的减小，因而器件的迁移率随Nb掺杂量的增加而增大。但是，当Nb掺杂量较大时，二维NbxW1-xS2的稳定性变差，结晶质量下降，使得晶界对载流子的散射作用增强，导致FET的载流子迁移率下降。此外，高的Nb掺杂浓度会形成较多的深能级缺陷以及较高的费米钉扎效应。因而，在Nb掺杂量较高时，二维NbxW1-xS2 p-FET器件的迁移率降低。本项目成功揭示了p型二维NbxW1-xS2外延生长规律及其p-FET器件电学特性的影响机理。