Study On The Photoelectric Detection Properties Of Tungsten Sulfide And Its Alloys Materials Synthesized By CVD Method

Two-dimensional transition metal dichalcogenide?TMDC?,the most common of which are WS₂ and MoS₂,open up a new way for the next generation of optoelectronics due to their unique properties such as optical transparency,high carrier mobility,wide-band tunable bandgap and strong optical interaction.In this paper,based on the layer number and alloying to adjust the electronic band structure of the material,for studying the photoelectric detection properties,mainly by using chemical vapor deposition?CVD?,through regulating the growth conditions,synthesis of monolayer WS₂,bilayer WS₂ and multilayer WS₂ crystal,furthermore,synthetic single-layer Mo_1-x-x W_xS₂ gradient alloy,and their photodetection properties is studied.The main research contents are as follows:?1?Large-area bilayer and monolayer tungsten sulfide?WS₂?crystals were grown by modified chemical vapor deposition method.Crystal structure and physical properties were studied by Raman and photoluminescence?PL?spectroscopy.The grown bilayer and monolayer tungsten sulfide?WS₂?crystals were found to have higher quality.Next,the photodetection properties of bilayer and monolayer tungsten sulfide?WS₂?phototransistors were compared.It was found that the bilayer tungsten sulfide?WS₂?phototransistor exhibited excellent photodetection properties,and its photoresponsivity,photoconductive gain and photodetection were respectively up to³×10³ A/W,1.4×10⁴and⁵×10¹² Jones.Moreover,the photoresponsivity of the bilayer WS₂ phototransistor can be further increased to 1×10⁴ A/W by gate voltage regulation.In addition,the bilayer WS₂ phototransistor exhibits a high response speed of less than 100?s,a large bandwidth of 4 kHz,high cycle reliability of over 10⁵ cycles,and spatially uniform light responsiveness.?2?2H and 3R stacked multilayer tungsten sulfide?WS₂?crystals were grown on a large scale by two-step chemical vapor deposition.The multilayer WS₂ crystals were characterized by aberration-corrected scanning transmission electron microscopy?AC-STEM?.High angle annular dark field?HAADF?images identified these two stacking methods;the layer number and stacking effect of multilayer WS₂ crystals were studied by Raman and photoluminescence spectroscopy.In addition,the circularly polarized luminescence from two stacked WS₂ crystals under circularly polarized excitation was also investigated,showing that these CVD-grown multilayer WS₂ crystals have significant spin or valley polarization.Finally,the photodetection properties of some layers?2H and 3R?stacked WS₂ crystals was initially explored.?3?We design a facile method to grow gradient alloying of Mo_1-x-x W_xS₂ monolayers with large domain sizes?lateral dimension up to 300?m?and high crystal qualities via chemical vapor deposition technique.Raman and photoluminescence spectroscopy and aberration-corrected scanning transmission electron microscopy?AC-STEM?were used to characterize the growth of a monolayer Mo_1-xW_xS₂ alloy with a gradient composition W from x=⁰ to¹ in a single region,and the span in bandgap can be readily tuned.Owing to the grading in band offsets,the compositionally graded Mo_1-x-x W_xS₂ alloy monolayer exhibits an excellent rectifying effect with the ratio of forward to reverse current up to¹0⁴.In addition,phototransistors based on the compositionally graded Mo_1-xW_xS₂monolayers exhibit a high responsivity up to 298.4 A/W in the visible light regime,and particularly a decent responsivity of 28.7 A/W in the near-infrared regime?1064 nm?,due to the injection of hot electrons.