The Study Of CVD Synthesized MoS₂ Films And Its Plasma Doping Under Magnetic Control

Two-dimensional（2D）transition metal dichalcogenides（TMDs）have been widely studied by scholars all over the world due to their natural band gaps,layered properties,and excellent electrical properties.MoS₂is one of the earliest materials studied in TMDs family.The single layer MoS₂ film is only atomic thick and shows a direct band gap of1.8eV.The great mechanical ductility,optoelectronic properties,and catalytic properties of MoS₂ films have attracted widespread attention in various fields.Preparing high-quality and large-area MoS₂thin films and effective low damage p-type doping are the basis for realizing its practical application.Among variety methods for preparing MoS₂ thin films,chemical vapor deposition（CVD）has become one of the most important ways for preparing MoS₂ films due to its simplicity,low cost,and high controllability.However,the traditional CVD method,which controls parameters such as the amount of source,temperature,pressure,and gas flow rate,appears to be inadequate for growing large-area MoS₂ films.In this article,the"face-down"CVD method is used.By adding a halogen salt（mainly Na Cl）to the molybdenum source,the molybdenum source’s melting point can be reduced by generating molybdenum chloride oxide,and the increasing of the molybdenum source vapor pressure can accelerate the reaction rate to achieve the large-area growth of MoS₂ films.At the same time,the generated MoS₂will cover the molybdenum source and hinder the progress of the reaction.This article proposes to replace the slide in the"face-down"method with a molybdenum sheet.By forming a system of Mo,MoO₃,and MoS₂,the weak reducibility of Mois used to make the reaction keep on.And through this method,large size and dense MoS₂ films were obtained.The plasma implantation method is widely used in the preparation of silicon-based devices and circuits due to its high efficiency and controllability.In the research of plasma doped TMDs thin films,due to the characteristics of the atomic layer thickness of TMDs thin films,low-damaged doping method has become a research direction in recent years.In this article,the nitrogen plasma doping MoS₂ films using a toroidal-magnetic-field is studied to achieve p-type doping of MoS₂ films.Firstly,by first-principles calculations,it was found that N⁺ions are the main cause of damage to MoS₂ films in nitrogen plasma.through the theory analysis,it’s feasible to adjust the concentration of N⁺and N₂⁺ions of nitrogen plasma by controlling the RF power supply voltage.Experiments were designed to achieve low-damaged p-type doping of the double-layer MoS₂ films.At the same time,the composition of nitrogen plasma and effective p-type doping at different powers were characterized by AFM,Raman,PL and XPS analyses.A p-type field effect transistor was fabricated and characterized.The hole mobilityμ_h-FE=24.32cm²V^-1s^-1,the threshold voltage about-2.6V,and the current switching ratio 10⁵ were obtained.