Construction Of Monolayer MoS₂ Field-Effect Transistors And Modulation Of Electric Transport Performance

Transition metal chalcogenides have attracted wide attention due to their unique layered material structure and physical properties.In particular,monolayer molybdenum disulfide(MoS2),as a wide band gap,atomic-level thickness,high mobility semiconductor material,is very suitable as a channel material for field effect transistors to construct high-switching ratio and high-performance electronic devices.Monolayer MoS2 field-effect transistors(FETs)can effectively suppress the short-channel effect caused by the shrinkage of the channel size,and thus show great potential in future chip and integrated circuit applications.However,there are many problems in monolayer MoS2 FETs,such as low mobility and low saturated output current caused by excessively high contact resistance.In this paper,monolayer MoS2 was used as the research object,and high-quality monolayer MoS2 was controlled and synthesized;The influence mechanism of different work function metals on the contact performance of monolayer MoS2 FETs was revealed,and the monolayer MoS2 FETs with metal gadolinium(Gd)as the electrode were constructed;The sulfur vacancy control strategy was used to optimize the electrical transport performance of monolayer MoS2 FETs,which provides an effective solution for the construction of high-performance monolayer MoS2 FETs;The electrical transport performance of the designed and constructed monolayer MoS2 FETs with edge contact remained stable under the small-length electrode,and finally monolayer MoS2 FETs with high-performance,small-length electrode had been fabricated.Firstly,monolayer MoS2 was prepared by oxygen-assisted chemical vapor deposition method and mechanical stripping method,and the preparation process parameters were optimized.It was found that the vertical growth of oxygen-limited monolayer MoS2 was the key to achieving large-area monolayer MoS2 growth.The precise transfer of the monolayer MoS2 was realized.The key factor affecting the morphology of the monolayer MoS2 is the temperature of the sulfur source,and the main factor affecting the crystalline quality of the monolayer MoS2 is the flow of oxygen.Secondly,monolayer MoS2 FETs with different metal contact electrodes by using different work functions were designed and constructed,and the law for the influence of metal work function on the electrical transport performance of monolayer MoS2 FET was revealed.It was found that metals with low work function can improve the electrical transport performance of monolayer MoS2 FETs.The monolayer MoS2 FET with low work function Gd as the electrode had excellent electrical performance,with a maximum mobility of 92 cm2V-1S-1 and a maximum saturated output current density of 289 ?A/?m.Thirdly,a method for regulating the concentration of sulfur vacancies in monolayer MoS2 was designed and developed,and the law and mechanism for the influence of the concentration of sulfur vacancies in contact region on the electrical transport performance of monolayer MoS2 FETs were studied and clarified.A weak argon plasma was used to control the concentration of sulfur vacancies in the contact region,and it was found that the significant n-doping effect caused by a large number of sulfur vacancies significantly increased the electron injection in the contact region,which reduced the Schottky barrier height to 17.8meV and reduced the contact resistance to 1.7 k?·?m.As a result,monolayer MoS2 FETs had excellent electrical transport performance,with a carrier mobility of 153 cm2V-1S-1,a saturation current density of 342 ?A/?m,and a switching ratio of 109.Finally,monolayer MoS2 FETs with edge contact were designed and constructed,and the electrical properties of monolayer MoS2 FETs with edge contact and top contact under different electrode lengths were studied and compared.The MoS2 FETs with edge contact exhibited low contact resistance of 2.5 kQ·?m,high carrier mobility of 96 cm2V-1S-1 and high switching ratio of 108.Since the edge-contacted monolayer MoS2 FETs still maintain good electrical stability at small electrode lengths,a small-size monolayer MoS2 FET by using an edge contact with a channel length of 90 nm and an electrode contact length of 185 nm had been constructed,with a maximum saturation current density of 730 ?A/?m,and an on-state current density of 178?A/?m.