The Study Of The Preparation Of Two-dimensional MoS₂ Films And Its Doping Properties

Two-dimensional?2D?transition metal dichalcogenides?TMDs?have recently attracted significant attention due to their unique material properties and potential applications in prolonging the Moore's law.Molybdenum sulfide?MoS2?is a representative of these materials.Monolayer MoS₂ films have the thickness of three atomic layer?7.5??and the direct band gap of 1.8 eV,which results in distinguished electronic and opoelectronic characteristics.The controllable growth and effective p-type doping of MoS₂ films is fundamental to its application.Chemical vapor deposition?CVD?is getting an upsurge of interest for synthezing MoS₂ films with high quantity.The concentration of molybdenum?Mo?source is a determining factor to the morphology of as-grown MoS2 films.In this research,we quantificationally analyse the evaporation process of Mo source,and fabricate the model for the concentration distribution of Mo source on the substrate surface.The model shows that the concentration of Mo source gradually decreases from center to edge of the substrate.The morphological changes of CVD synthesized MoS2 films validate the correctness of this model,and indicate the corresponding relationship between the morphologies of MoS₂ films and the concentration of Mo source.The results show that the optimum MoO₃ concentration for the growth of monolayer MoS₂ films is in the range of 3.72-4.04 g/m².Plasma doping has became the most promising candidate for TMDs doping due to its high controllability,excellent selectivity and compatibility with conventional complementary metal-oxide-semiconductor fabrication processes.In this research,we achieve the effective p-type doping using toroidal-magnetic-field controlled oxygen plasma on the MoS2 films.The theoretical calculation indicate the toroidal-magnetic-field can enhance the ratio of O2⁺ions,which lead to a shallow acceptor level at 42.16 mV above the valance band maximum and extracting excess 1.0e from MoS₂ lattice.The effective p-type doping is demonstrated by Raman spectroscopy,photoluminescence spectroscopy and X-ray photoelectron spectroscopy.Also,the fabricated bottom-gated MoS₂ field-effect transistor shows a current on-off ratio of 10⁷,a hole mobility of 115.2 cm²V^-1s^-1 and a subthreshold swing of 137 mVdec^-1 at room temperature.These findings provide a scheme for realizing two-dimensional integrated circuit and excellent optoelectronic devices using MoS2 and other homogeneous TMDs.