Controllable Manufacturing,related Properties And Device Construction Of MoS₂ Film Obtained By Atomic Layer Deposition

The special structure of MoS₂ endows it with excellent electrical,photoelectric and mechanical properties.Atomic layer deposition（ALD）there is a feature that thickness of obtained film can be controlled in atomic scale.According to the feature,bulk and mono/few layer MoS₂ films were fabricated by adjusting process parameters.Then,mechanical friction,piezoelectricity,and field effect of obtained MoS₂ films were observed,and the innovative results are as follows:（1）Bulk and mono/few MoS₂ films were fabricated by adjusting process parameters.Then,the obtained films were observed by a variety of methods,in which the influence of key parameters on the film quality was studied and determined.When MoCl₅ and H₂S are used as the source,the optimum pulse and purge time are 0.5s,30s,0.5s,30s.Temperature window of ALD is 430-470°C,in which the film has a higher crystallinity.The growth rates of the films on the silicon and alumina substrates are 3.8?and 4.3?at 460°C respectively.As substrate,alumina is more suitable for growing MoS₂ films than silicon,because there are more hydroxyl functional groups on the surface.The mono/few MoS₂ films were prepared by using silica as the substrate.The growth process and mechanism were observed.It is found that monolayer MoS₂ can be obtained by 1-ALD-cycle.After 2-ALD-cycle,the superposition of MoS₂ grain appears,indicating that the density and thickness of MoS₂ increase at the same time.At least 4 ALD cycles are needed to form a compact and continuous MoS₂ film.Thickness of the film can be controlled by the number of ALD cycles（NC）.（2）Frictional properties of MoS₂ films with different thicknesses obtained by ALD were observed respectively.It is found that bulk MoS₂ films on silicon substrates can effectively reduce the friction force by 30-45%.Moreover,the friction properties of mono/few layer MoS₂ films on silica substrates change with the NC.When the NC is in 3-10,the friction force can be reduced by 40-54%.MoS₂ film obtained by ALD can not only ensure the excellent lubrication performance of interlayer interface but also effectively avoid the"wrinkle"phenomenon.（3）The size-dependent piezoelectricity of MoS₂ films with different thicknesses obtained by ALD was observed respectively.It is found that the grain size of MoS₂ film can be controlled by changing the growth temperature of ALD.The piezoelectric measurement results show that the grain size has a very important influence on the piezoelectric coefficient.When the grain size is less than 120 nm,the piezoelectric coefficient increases with the increase of grain size.With the increase of film thickness,the piezoelectric constant increases first and then decreases.Therefore,the piezoelectric coefficient of obtained MoS₂ can be adjusted by changing the growth temperature of ALD and applying different ALD cycles.（4）MoS₂ film obtained by ALD was applied to fabricate field effect transistor（FET）,and performance of the FET was measured.MoS₂ film obtained by ALD has uniform quality and large coverage area,so it is easy to fabricate FET devices.According to the obtained FET,the contact between electrode and channel is ohmic contact.The obtained MoS₂ is P-type,and its carrier mobility is lower than that of MoS₂ obtained by mechanical stripping or chemical vapor deposition.The carrier mobility decreases with the increase of channel length,which is due to nanocrystalline structure of MoS₂ obtained by ALD.At the same area,the defect density such as grain boundary will be greater,thus reducing the field effect characteristics.In conclusion,bulk and mono/few MoS₂ films were controllably fabricated by ALD.Then,the mechanical friction and piezoelectric properties of the films were observed.Moerover,the exploratory research on MoS₂ FET will provide useful theoretical and experimental accumulation for the design and manufacture of MoS₂ devices in the future.