摘要
自从范德瓦尔斯异质结概念被提出来后，其优异的光电性质就吸引了科学界
的广泛关注。在这几年间，关于异质结的新机理和新器件的探索一刻也没有停止，
成为当前凝聚态物理研究领域的前沿和焦点。论文首先介绍了相关实验方法，然
后对WSe2和石墨烯这两种二维材料的基本输运特性进行了研究，最后制备出背栅型WSe2/石墨烯异质结场效应晶体管，并探讨了其光电响应的机理。本文的主要工作及结论如下：
（1）利用微机械剥离法和定点转移技术成功制备出WSe2/石墨烯异质结，并通过标准微纳器件工艺加工制备出基于二维材料及其异质结的背栅型场效应晶体
管器件。利用拉曼光谱、原子力扫描等多种手段对材料进行了较全面的表征。
（2）研究了石墨烯和WSe2的基本电学性质和光电特性。结果表明石墨烯具有极高的载流子迁移率和电导性，但是开关比较低，并且光响应度极低。WSe2载流子迁移率较低，但开关比极大，而且具有很好的光电响应特性。
（3）成功制备出WSe2/石墨烯异质结背栅型场效应管器件，对其基本场效应特性曲线和光电响应特性进行了全面的测量。实验结果表明器件具有良好的光电
探测能力。在测试中，发现WSe2/石墨烯异质结在光照下时呈现出反常的转移特性曲线。于是我们提出WSe2/石墨烯异质结中可能存在电-光双调制效应对能带偏移进行影响，从而定性地解释了这一新奇的物理现象。
（4）利用紫外臭氧清洗技术解决了定点转移中的残胶问题。通过实验，发现
残胶的存在确实会导致金属和石墨烯之间接触不良。不过采用紫外臭氧清洗处理
后，可以有效地清除这种残胶，从而提高载流子的迁移率。
主题词：石墨烯；WSe2；异质结；定点转移；场效应管；光电特性
ABSTRACT
Since the concept of van der Waals(vdW)heterostructures based on two-dimensional(2D)materials was put forward,it has attracted a wide range of scientific research as a result of excellent photoelectrical properties the heterostructures performed.In this paper,we introduced the experimental methods and techniques at first,and then studied the basic transport properties of WSe2and graphene.Finally, back-gated field-effect transistors based on WSe2/graphene heterostructures were fabricated,and the photoelectrical properties were systematically discussed and investigated.The main work and conclusions of this paper are as follows:
(1)WSe2/graphene heterostructures were successfully prepared by mechanical exfoliation and deterministic transfer method.Next,the devices were fabricated by standard micro-nano technology.The materials were comprehensively characterized by Atomic Force Measurement,Raman spectrum and so on.
(2)The basic transport properties of graphene and WSe2were studied.The results indicate that graphene owns high carrier mobility and conductivity,but the on/off ratio and the photo responsivity is extremely low.In contrast,the carrier mobility of WSe2is relatively low,but WSe2has good photoelectric response and on/off ratio.
(3)The device based on WSe2/graphene heterostructures was successfully fabricated.Its fundamental field-effect characteristic and photo-response performance were systematically studied.In the test,WSe2/graphene heterostructures exhibited an abnormal transfer characteristic under illumination.Therefore,we propose a mechanism named electro-photo modulation of the band offset in WSe2/graphene van der Waals heterostructures to explain this novel phenomenon.
(4)We put forward a rapid and effective way named ultraviolet-ozone treatment to reduce the negative effect of adhesive residue existing in deterministic transfer method. The results indicate that this adhesive residue may cause poor contact between metal and graphene,thus greatly degenerating the performance of the device.However,this unpleasant influence could be reduced effectively by adopting ultraviolet-ozone treatment.
Key Words：Graphene,WSe2,Heterostructures,Deterministic Transfer Technique,Field Effect Transistors,Photoelectrical Properties