Investigate The Effect Of Alumina Stress Layer On The Material And Photodetector Performance Of Layered Molybdenum Sulfide

As a typical representative of layered two-dimensional(2D)materials,molybdenum sulfide(MoS₂)has attracted wide attention in the application of optoelectronic devices due to its excellent mechanical properties and adjustable band gap.In particular,the huge potential of the monolayer MoS₂ with a direct band gap is released due to its higher semiconductor quantum efficiency and excellent response performance in the visible light band.However,so far,the detection capability of MoS₂ has been limited due to the difficulty in preparing large-scale,high-quality monolayer MoS₂ and the performance of fabricated photodetectors is very sensitive to the surrounding environment due to the large surface to volume ratio.Therefore,how to improve the quality of MoS₂ film and its photoelectric performance needs our future efforts.In this paper,we discussed the growth process of large-scale monolayer MoS₂ and the effect of aluminum oxide(Al₂O₃)stress layer on the thermal and photoelectric properties of the film.In this paper,a chemical vapor deposition(CVD)method was used to explore the optimal growth conditions for MoS₂ deposition on a sapphire substrate at 750?using 5 mg of MoO₃and an Ar flow rate of 80 sccm.The thickness of the grown MoS₂ is a monolayer with good uniformity and quality,which has been verified by AFM,TEM,Raman spectroscopy,and other methods.Subsequently,we used the atomic layer deposition(ALD)method to deposit a layer of Al₂O₃ with a thickness of about 3 nm on the surface of a large-scale monolayer MoS₂,and compared the performance changes of MoS₂ with and without Al₂O₃ stress layer.Compared with the Raman spectrum at room temperature,MoS₂ has a red shift on the¹₂₂)Raman mode peak after the Al₂O₃ stress layer is deposited,which indicates that MoS₂ has tensile stress and leads to an increase in its absorption capacity.Compared with the temperature-dependent Raman spectrum,the Al₂O₃ stress layer reduces the red shift of the two vibration mode peaks(¹₂₂)and₁₂))of MoS₂ with increasing temperature,which is due to the thermal stability of MoS₂ is improved.In this paper,we also discussed the change of the photoelectric performance of the monolayer MoS₂ photodetector under the action of the Al₂O₃ stress layer.Compared with the absence of Al₂O₃,the current of MoS₂ photodetectors with a 3 nm thick Al₂O₃ stress layer is more than 10 times higher under the light of 460 nm and 660 nm,which is attributed to the stretching induced by Al₂O₃ on the MoS₂ surface.At the same time,dark current is also increased due to the reduced band gap caused by this tensile stress.Analyzed the current of the photodetector under varying luminous power,MoS₂ with Al₂O₃ stress layer displayed a state-of-the-art performance with a responsivity of 16.103 A/W,a Gain of 191.80,a noise equivalent power(NEP)of 7.96×10^-15 W/Hz^1/2,and a normalized detectivity of 2.73×10¹⁰Jones.The current rise time of the photodetector is also significantly shortened since the electron mobility is improved on tensile stress introduced by Al₂O₃.We hope the research result of this paper will provide guidance for the application of MoS₂ in next-generation imaging systems.