Preparation And Optoelectronic Properties Of Monolayer Molybdenum-based Chalcogenides And Their Heterojunction

Two-dimensional?2D?semiconductors are expected to be used in next-generation electronic devices due to their unique structure and excellent physical properties.The controllable preparation of the large-scale and high-quality 2D semiconductors is still one of the research hotspots.In this paper,single-layer MoS₂,MoSe₂ and SnS₂/MoSe₂ van der Waals heterojunctions were synthesized by chemical vapor deposition?CVD?.Their electron transport and optoelectronic properties were studied.Firstly,the water-assisted CVD method has been developed to grow high-quality single-layer MoS₂ with clean surface,uniform distribution and large scale.Field effect transistors?FETs?were fabricated and their optoelectronic properties were measured.The results show that the water-assisted grown MoS₂ FET has large drive current and high mobility(25 cm² V^-1 s^-1),as well as a high ON/OFF current ratio?10⁸?.In addition,the transistor exhibits good photoresponse properties to 532 nm laser.Secondly,single layer MoSe₂ and atomically thin SnS₂ films were synthesized by CVD method.The synthesized single-layer MoSe₂ has a large area,uniform dispersion and high crystal quality.The MoSe₂-based FET exhibits excellent electron transport performance.Continuous SnS₂films with multilayer domains on top surface were obtained,and their electronic and optoelectronic properties were investigated.The SnS₂-based FETs show ON/OFF current ratio of 10² and good photoresponse properties.Finally,SnS₂/MoSe₂ van der Waals heterojunctions was prepared by a two-step CVD method.The morphological,structural characterization and optoelectronic properties of the as-synthesized heterojunctions were investigated.The results indicate that the heterojunctions are clean and uniform,and have high crystal quality.Besides,the heterojunctions exhibit bipolar behavior.