Research On The Synthesis,Modification And Devices Of Monolayer Molybdenum Disulphide

Monolayer molybdenum disulfide（MoS₂）,a new type two-dimensional semiconductor with excellent in mechanical,electrical and optical properties,has become one of the research highlights.However,it still has many unclear properties and unsolved problems,for example,growth mechanism of monolayer MoS₂ in chemical vapor deposition（CVD）,contact resistance between MoS₂ and electrode,ultrashort channel length MoS₂ field effect transistors（FETs）,and so on.Here,we mainly research on growth MoS₂ by CVD,phase transition of monolayer MoS₂ and fabrication of sub-10MoS₂ FETs.We use molybdenum trioxide powder（MoO₃）and sulfur powder as predecessors,obtain plenty of large-size monolayer MoS₂ in argon atmosphere by CVD.The growth of MoS₂ is very sensitive to the amount of predecessors.The size of MoS₂ will increase until a maximum while the sulfur increase.The size and occupancy of MoS₂ will increase while the MoO₃ increase,intermediate will also increase at the same time.The higher of growth temperature,the larger of MoS₂ size.But when growth temperature exceeds the best temperature,multilayer MoS₂ will be grown.Furthermore,the wettability of substrate effects growth of MoS₂ as well.Lastly,growth of MoS₂ by CVD is introduced on multi-fin substrate and monolayer MoS₂ is grown along the surface of multi-fin substrate.With the results of Raman spectrum,transmission electron microscope（TEM）and electrical properties,we confirm that the phase transition of CVD monolayer MoS₂ can be induced by potassium iodide（KI）solution.Comparing with other solutions’effects on MoS₂,we find that both iodide ions and defects of MoS₂ are the key factors for MoS₂phase transition.What’s more,we develop a photoresist-free method for MoS₂ transfer.Using this method,suspended MoS₂ is obtained and measured by transmittance spectrum.We fabricate electrodes with nanogaps by using horizontally aligned single-wall carbon nanotubes（SWCNTs）as evaporating mask.According to experimental results,parameters of fabrication don’t have much influence on the size of nanogaps,so this method has a large process window.A sub-10 nm MoS₂ FET is fabricated by those nanogap electrodes.FET shows a good immunity to short channel effects with on/off ratio ～10⁷,subthreshold swing ～120 mV/dec,mobility ～17.4 cm²/V×s and DIBL ～140 mV/V.In the end,MoS₂ FET based on monolayer MoS₂ grown at multi-fin substrate with aspect ratio of 1:1 is obtained and it has 2 times current density than planar MoS₂ FET.