The Fabrication Of MoX₂(X=S,Se)Nanofilm Heterojunction For Electronics And Optoelectronics

Transition metal dichalcogenides,as a kind of a graphene-like layered materials,have become a new class of nanomaterials with promising applications for exploring novel physical phenomena and mechanisms,because of the common characteristics of the atomic-scale thickness,tunable band gap and good electrical conductivity.Compared with traditional semiconductor silicon and germanium,molybdenum disulfide(selenide)molybdenum(Mo X₂(X=S,Se))material with good visible light-near-infrared light absorption and excellent electrical conductivity has the characteristics of tunable band gap.Therefore,there are new possibilities in 2D-3D heterogeneous micro-nano optoelectronic devices.In this paper,the synthesized large-area Mo X₂(X=S,Se)nanofilms with different properties are used as the research basis.Subsequently,a large-area Mo X₂(X=S,Se)nanofilm was directly grown on silicon(Si)with a silicon dioxide(Si O₂)insulating layer window to form a heterojunction optoelectronic device.Subsequently,the heterojunction optoelectronic devices were formed by directly growing large-area Mo X₂(X=S,Se)nanofilms on silicon(Si)with silica(Si O₂)insulating layer window.Then,the photoelectric response characteristics of Mo X₂(X=S,Se)/silicon heterojunction photodetector were explored through the built photoelectric performance test platform.The main research contents and conclusions are as follows:(1)Preparation and characterization of large-area vertically aligned molybdenum disulfide(V-MoS₂)nanofilms.The pre-deposited Mo film was sulfurized in a three-temperature zone high-temperature tube furnace by chemical vapor deposition(CVD)to obtain a large-area MoS₂ film with uniform color.The grazing incidence angle X-ray diffraction pattern(GIAXRD),transmission electron microscopy(TEM),high resolution-transmission electron microscopy(HRTEM)and X-ray photoelectron spectroscopy(XPS)were used to characterize the microstructure and main structural components of MoS₂ thin films.Raman peaks,film thickness and roughness of MoS₂ thin films were characterized by Raman spectroscopy,atomic force microscopy(AFM)and scanning electron microscopy(SEM).The relationship between the thickness and absorbance of MoS₂ film was analyzed by UV-Vis spectrophotometer.(2)Study on the optoelectronic properties of MoS₂/Si heterojunction photodetectors.The optoelectronic properties of two V-MoS_2/n-Si and V-MoS₂/p-Si heterojunction photodetectors fabricated by depositing 20 nm thickness V-MoS₂ nanofilms on Si wafers layers were tested.The V-MoS₂/n-Si shows superior responsivity(5.06 m A/W),good photodetectivity(5.36×10¹¹ Jones),high on/off ratio I_on/I_off(8.31×10³ at 254 nm)and a fast response speed with the rise time and fall time being 54.53 ms and 97.83 ms,respectively.In contrast,the V-MoS₂/p-Si device has poor performance,with a responsivity of 0.16m A/W,a photodetectivity of 1.68×10⁸ Jones,and a rise time of 150 ms under-2 V bias.(3)Preparation and characterization of large-area selenium-deficient(Se-deficient)molybdenum diselenide film nanofilms.Based on the the selenization of Mo film method,large-area continuous MoSe₂ was synthesized by low-pressure CVD and atmospheric-pressure CVD,respectively,and it was observed that the films prepared by the former were more uniform.The growth environment of selenization was controlled by adjusting temperature,argon flux and selenium source quality,so as to obtain the high-quality MoSe₂ films.The structure,defects and Mo:Se element ratio of MoSe₂ thin films were characterized and simply analyzed by GIAXRD,Raman spectroscopy and XPS.The thickness of the prepared MoSe₂ nanofilm was determined by cross-section SEM,and the effect of 40 nm and 130 nm MoSe₂ nanofilm on the absorption rate of Si was tested by UV-Vis spectrophotometer.(4)Study on the optoelectronic properties of MoSe₂/Si heterojunction photodetectors.The optoelectronic properties of MoSe₂/n-Si and MoSe₂/p-Si heterojunction photodetectors fabricated by depositing 40-nm and 130-nm thickness Se-deficient MoSe₂ nanofilms on Si wafers layers were tested.Four lasers(450,638,980 and 1310 nm)with low power density were used for the test,the results showed that Se-deficient MoSe₂/Si only had obvious photoresponse to 980 nm,and the thickness of 40 nm MoSe₂ was superior.When the MoSe₂ thickness is kept at 40 nm,the Se-deficient MoSe₂/p-Si with better performance exhibits a responsivity of 57.2 m A/W and rise/fall time of 132/256 ms.