Oxygen-Regulated Growth-Etching Mechanism And Optoelectronic Properties Of Two-Dimensional Transition-Metal Dichalcogenides

Two-dimensional transition metal dichalcogenides（TMDS）have showed great potential in the field of high-performance micro-nano electronics and optoelectronic devices due to their unique structure and excellent photoelectric properties.The controllable preparation and tunable electronic properties of 2D TMDs are the i mportant basis for their device applications.Chemical vapor deposition（CVD）is the most mainstream method for preparing high quality 2D TMD materials,but the conventional methods are easy to cause TMD domain in size,thickness and distribution of the substrate surface are not uniform,resulting in the formation of defect density is high,and the crystal quality is poor,which greatly limits their applications in the field of optoelectronic devices.Therefore,this paper develops short-range near-steady spatial growth strategies for supply and limited domain,the role of oxygen in the g rowth and etching of 2D TMD materials was systematically studied,and explored the intrinsic mechanism of oxygen doping and alloying in regulating the band structure and pho toelectric properties of 2D TMD materials.The main research contents include:1.Based on the oxygen-assisted CVD method,the growth mechanism and the effect of components on the photoelectric properties of Mo S_2（1-x）Se_2xalloy monolayer under short-range vertical near-steady supply strategy were systematically studied.Investigated the effects of oxygen and molten salt concentration on the structure and morphology of Mo S_2（1-x）Se_2x alloy monolayer.The results show that the rapid and high-quality growth of monolayer Mo S_2（1-x）Se_2x crystal is due to the synergistic effect of oxygen carrier gas and sodium bromide additive under vertical short-range near-steady state supply condition.Large size and high quality monolayer alloy films can be prepared by adjustin g the oxygen flow rate and the ratio of sodium bromide to growth source.Meanwhile,the mass change of the selenium source can change the band struc ture and optical properties of the monolayer Mo S_2（1-x）Se_2x,so that the band gap can be continuously tuned between Mo S₂ and Mo Se₂.This work provides an important basis for the high quality preparation of 2D TMD alloys and the control of their photoelectri c properties.2.We investigate the structure,morphology and optical properties of Mo S₂,WS₂ and their heterojunctions under different oxygen etching conditions.The evolution mechanism of oxygen etched 2D TMD materials and its correlation with photoelectric properties are revealed.The results show that the structure,morphology and properties of 2D TMD materials are closely related to the conditions of oxygen etching.Under the condition of low concentration and finite time,oxygen molecules are easily doped into the crystal lattice of Mo S₂,which can improve the exciton luminescence intens ity.With the increase of the concentration and etching temperature,these materials show significant etching orientation,resulting in the formation of uniformly oriented triangular etching holes,which are concentrated near the grain boundary.In addition,the oxygen etching rate of these TMD materials is closely related to the metal-chalcogenide atom interaction,which makes Mo S₂exhibit better oxidation resistance th an WS₂.This study provides an important basis for understanding the oxygen etching mechanism of 2D TMD materials and its application in optoelectronic devices.