Study On Low Power Sputtering Deposition And Crystallization Of Few-layer MoS₂ Films

As a two-dimensional semiconductor material,the few-layer Mo S₂ film has the characteristics of tunable band gap in the range of 1.2～1.9 e V,large carrier mobility,and huge light absorption in the visible light range.It is widely used in field effect transistors,flexible devices,optoelectronic devices,etc.The field has broad application prospects.At present,the common method for preparing few-layer Mo S₂ thin films is chemical vapor deposition,which is difficult to achieve large-scale preparation and requires multiple transfers to prepare field effect transistors devices.In comparison,sputtering,as a thin film preparation method with simple operation and low requirements on substrates,is easier to achieve large-scale controllable preparation of Mo S₂ thin films,and to achieve transfer-free preparation of field effect transistors devices.In this paper,Mo S₂ thin films were prepared on soda-lime glass substrates and P-type Si（100）by low-power radio frequency magnetron sputtering combined with sulfidation.By means of Raman spectroscopy,UV-vis absorption spectroscopy,45°specular reflection spectroscopy,atomic force microscopy and other characterization methods,the effect of annealing process on the formation of Mo S₂ thin films with different sputtering times on soda-lime glass substrates and P-type Si（100）substrates were systematically studied.The influence of morphology,thickness,structure,and optical properties were investigated,and the electrical properties of few-layer Mo S₂ thin films were also explored.The main findings are as follows:（1）Low RF（radio frequency）power magnetron sputtering can control the thickness of Mo S₂ film more accurately.In this paper,bilayer,tri-layer and five-layer Mo S₂ were successfully fabricated on soda-lime glass substrates and P-type Si（100）substrates with2,4,and 6 minutes of sputtering time at 15W RF power.（2）The results of spectral analysis show that the Mo S2 films deposited by sputtering are amorphous.After annealing,the 2H-Mo S₂ is transformed into a crystalline state.Atomic force microscopy（AFM）shows that the annealed films on the soda-ca glass and P-type（100）silicon substrates are granular films.Raman spectra show that the thin films with fewer layers on the sodium-calcium glass substrates can obtain better crystallization effect at 500～580℃,while the samples on the P-type（100）silicon substrates need higher annealing temperature（≥700℃）to achieve better crystallization effect.（3）By exploring the electrical properties of Mo S₂ thin films,it is found that the few-layer Mo S₂ thin films have high resistivity,and the resistivity of Mo S₂ thin films with a thickness of about 1 nm is as high as 10⁴Ω·cm after high temperature annealing.Attempt to construct a thin film field effect transistor with Mo S₂ film as channel material,and found that the constructed field effect transistor responds to the gate voltage,and its field effect mobility is calculated to be 0.675 cm²V^-1s^-1.