Preparation And Optoelectronic Properties Of Two-dimensional Tungsten Disulfide Doped With Niobium Atoms

In recent years,two-dimensional transition metal dichalcogenides（TMDCs）have been widely investigated for their unique properties.For example,WS₂ and Mo S₂ have excellent properties including tunable bandgap,high carrier mobility,and excellent light absorption,which make them attractive materials for electronics and optoelectronics.However,as TMDCs materials have been studied in depth,a single property no longer satisfies the requirements for the application of TMDCs materials.The preparation of high-quality two-dimensional alloy compounds by chemical vapor deposition,using doping and other means to modulate the bandgap and change the electrical transport properties,and improve the electrical and optoelectronic properties,can enable two-dimensional TMDCs materials with broader application prospects.In this study,monolayer Nb-doped WS₂ crystals were prepared via chemical vapor deposition（CVD）,and the factors affecting the morphology and doping concentration during the growth of Nb-doped WS₂ crystals were investigated,and the crystal structure of Nb-doped WS₂ was measured by Raman and PL characterization methods,and the electrical and optoelectronic properties were also investigated by fabricating field-effect transistors.（1）Large-size monolayer Nb-doped WS₂ crystals were successfully prepared on Si/Si O₂ substrates by chemical vapor deposition.The process parameters such as growth temperature,growth time,pressure and mass of precursors were controlled to achieve the modulation of the size and morphology of Nb-doped WS₂ crystals.And the gradient doped and uniformly doped samples were initially distinguished by different fluorescence intensities,which provide reference significance for the preparation of other two-dimensional doped TMDCs materials.（2）The doping of Nb atoms was determined by X-ray photoelectron spectroscopy（XPS）and transmission electron microscopy（TEM）studies,and the doping concentration of Nb atoms was calculated to be 5.48%,and the substitution type of Nb atoms was investigated;Raman studies found that Nb atom doping changes the Raman vibrational mode of WS₂;PL and absorption spectroscopy analyse found that Nb doping decreases the PL intensity and optical absorption properties of WS₂.（3）Monolayer WS₂ and Nb-doped WS₂ crystals were fabricated into field-effect transistors to investigate the transition from n-type to p-type semiconductors due to Nb doping into the lattice of WS₂.Meanwhile,Nb doping decreases the contact resistance and makes the ohmic contact between the device and the metal electrode,but Nb doping decreases the carrier mobility due to the existence of defects.The monolayer WS2 and Nb-doped WS₂ optoelectronic devices were constructed,and the optoelectronic performance parameters were calculated by conducting optoelectronic tests on the two devices using lasers of different wavelengths,and it was found that Nb doping decreases the optoelectronic performance of WS₂.