Control Growth And Properties Study Of Large-Scale Transition-Metal Dichalcogenides And Heterostructures

As the candidates for silicon-based materials in the future,two-dimensional materials have attracted the attentions of researchers since their discovery.Transition-metal dichalcogenides(TMDCs),as an important branch of two-dimensional materials,have unique application prospects in the field of optoelectronic devices.Controllable preparation of high-quality TMDCs materials is crucial for development of their integrated devices and industrialization.At present,TMDCs are mainly grown by CVD method,but the traditional CVD method has many shortcomings in gas flow and reactant distribution,which seriously affect the film size and crystal quality,and become the bottleneck restrncting the applications of TMDCs.In order to solve the above problems,our work focuses on experimental design,crystal growth,property characterizations,device fabrications and so on.Finally,controllable growth of large area and high quality TMDCs and their heterostructures are realized,and the wafer-scale two-dimensional device arrays are achieved.The main contents are as follows:1)Based on the analysis and optimization of traditional preparation methods,an improved CVD growth method combined with hot evaporation coating technology was proposed to regulate the growth of TMDCs two-dimensional materials.The results show that the growth temperature greatly affects the morphology,structure and quality of crystals,and the amount of reactants plays a key role in the nucleation density and grain size of materials.Based on the optimized growth temperature and the amount of reactants,the reduction gas H2 was introduced to control the growth rate and coverage.The wafer-scale continuous TMDCs films were successfully grown on SiO2/Si substrates.2)Raman,PL,TEM and STM were used to characterize the surface morphology,material composition,crystal quality,lattice structure and electronic properties of wafer-scale TMDCs monolayer.The results show that the TMDCs thin films have continuous monolayer thickness at wafer-scale,uniform and suitable material composition,high crystal quality,n-type band structure and reasonable optical and electrical band gap.Based on the wafer-scale continuous monolayer TMDCs,carge area FET arrays were successfully fabricated and the electronic transport characteristics were characterized.The results show that the carrier mobilitcies are concentrated in the range of 0.2-4.0 cm2V-1s-1.The values are superior to many reported results of CVD-WS2 devices,and even equal to the carrier mobility measured by mechanically exfoliated WS2 samples,which proves the excellent electrical properties of the wafer-scale TMDCs monolayer.3)Based on the successful growth of monolayer TMDCs two-dimensional material,a multi-component transition metal growth source was introduced to regulate the growth of TMDCs heterostructures by utilizing the competitive relationship in the growth process.Combining with the characterization of SEM images.Raman and PL spectra,it is found that the in-plane heterostructures were grown at the same proportion of various transition metal sources,while the vertical heterostructures were achieved at different proportion of various transition metal sources.On this basis,the composition of multilayer transition metal source films was adjusted and the in-plane superlattices were successfully obtained.