Growth And Characterization Of Rare Earth Ce Doped WS₂ Thin Film

Two-dimensional WS₂film has attracted great research interest for its potential application as optoelectronic devices due to its layer-dependent bandgap in visible and infrared range.Its ultrathin thickness results in a low absorption coefficient,which limits its optoelectronic application.It is known that rare earth elements have abundant energy levels.Thus,it is hopeful to renormalize the energy level of WS₂ film by doping rare earth elements to improve the optoelectronic properties.In this work,WS₂film is grown by Chemical Vapor Deposition(CVD)with charge materials of WO_2.9and S powders.During the growth,Na Cl was employed as the flux to decrease the growth temperature.By optimizing the growth parameters,large size monolayer WS₂ film with high quality was achieved.Then,Ce-doped monolayer WS₂film was grown using the mixture of WO_2.9and Ce₂(C₂O₄)_3·10H₂O and S powder as the charge materials with the same growth procedure as that of WS₂ film.The morphology,the composition,the structure and the optical spectra of the as-grown WS₂ film and Ce-doped WS₂ film were characterized.From the optical microscope and Atomic Force Microscope images of Ce-doped WS₂ film,it can be seen that the achieved thin film is a monolayer with high quality.The composition and structural tests of Ce-doped WS₂ film and WS₂ film were performed together.By their comparison,their Raman spectra give a larger Raman shift.Their results of High-resolution Transmission Electron Microscope and Electron Dispersion Spectroscopy measurements show that there is a lattice shrink after doping.Meanwhile,the tests of Selected Area Electron Diffraction pattern and X-ray Photoelectron Spectroscopy between them indicate that Ce atoms stay in the monolayer,and there is a chemical shift after doping.All the above results suggest that the obtained thin film is the Ce-doped monolayer WS₂.Comparing the PL spectra of Ce-doped monolayer WS₂ and monolayer WS₂,a clear PL redshift and a new radiation peak at 694 nm were obtained after doping.Besides,from the transient adsorption spectra,we can notice the enhanced adsorption from the doped monolayer.The renormalization of the band structures and the enhanced absorption of Ce-doped monolayer WS₂ may bring its potential application as a photodetector.This work is to be continued.