Investigation Of High Mobility MoS₂-field Effect Transistor

With the coming of 22 nm process nodes in Integrated Circuit,traditional silicon-based MOSFETs have ran into their bottleneck due to the attenuation of the device performance caused by short-channel effect,Thus,it is urgent to find novel materials to replace and continuing improve the performance of device.Transition-Metal Dichalcogenides have attracted extensive attention due to the unique property of physics and ultra-thin thickness.MoS₂,as one of materials in TMDs with large bandgap?1.2-1.8eV?,has potential application to be the material of channel for field effect transistors?FETs?,to form a high on/off ratio and low-power devices,which shows superior immunity to short-channel effects while also compatibility to traditional semiconductor process.Thus,large-area,layer-controllable growth of MoS₂ and performance optimization are necessary for the application of MoS₂-based field effect transistors.At present,Most samples of reserach on MoS₂-FET are prepared by mechanical exfoliation,the disadvantages of low yield and small-area limiting the application.Monolayer-MoS₂-based FETs always show low mobility(10-2¹0cm2V^-1s^-1)due to the extremely sensitive to the environment,High resistance of MoS₂-Metal contact and defects in MoS₂-channnel also limit the performance of MoS₂-FET.In view of above disscussion,we have worked on growth process optimization of large-size,layer-controllable MoS₂ and performance optimization of MoS₂-FET.In this dissertation,the main reserach contents are as follows: growth process optimization of CVD-MoS₂ for large-size and layer-controllable MoS₂;Fabrication of back-gated MoS₂-based field effect transistors by traditional micro-nano processing technology;reducing the contact of MoS₂-Metal contact and defects in MoS₂ channel to improve the performance of devices.Growth process optimization of CVD-MoS₂: Studying the effect of temperature and H2 flow on size and layer-number in growth of MoS₂,And we have got large-size?10?m⁶0?m?monolayer,bilayer MoS₂ flakes and less tri-layer?10¹5?m?,4-layers?⁵?m?MoS₂ flakes;The MoS₂ flakes show high quality measured by XPS,TEM and Raman spectrum.Fabrication of back-gated field effect transistors on 1-3 layers MoS₂ by photolithography,PVD for metal electrode and lift-off,studying the performance difference of?1-3 layers?MoS₂-FET.Based on the fabrication of MoS₂-FET,we also improved the performance of devices by chemical modification to reducing the contact resistance and defects in MoS₂ channel.On the one hand,reducing the resistance caused by Mo S₂-Metal contact by changing the 2H-MoS₂?semi-conduct phase?to 1T-MoS₂?metal phase?by n-butylithium,the transistors show 2X enhancement in mobility and on-current.On the other hand,we reduce the defects in MoS₂ by MPS-treated and annealed at 350?,then combining with 1T-MoS₂ contact,the devices show the mobility and on/off ratio of 50.23cm2V^-1s^-1 and 8×10⁶,respectively.