Controllable Synthesis And Opto-electronic Properties Investigation Of 1D/2D Heterostructures Based On CdS Nanowires And Ws₂ Nanosheets

Graphene as an ideal two-dimensional electronic material,with high mechanical strength and flexibility,unique energy band structure and excellent electrical properties,has been researched extensively by materials scientist both at home and abroad.However,graphene has a zero-band gap,which limits its use in optoelectronics.As a result,researchers have turned their attention to other two-dimensional graphene-like semiconductor materials,such as transition metal sulfides（TMDs）,transition metal oxides,boron nitride and black phosphorus,which have emerged in recent years.TMDS have received extensive attention and in-depth research in this huge two-dimensional semiconductor material system.The 2H phase TMDs are composed of VI group transition metal group elements（M:Mo and W）and sulfur group elements（X:S,Se,Te）.The monolayer TMDs have a direct band gap,which covers a wide band range from visible to near-infrared.More importantly,it is possible to control continuously the energy band of TMDs materials and to build the construction of planar and vertical heterojunctions by alloying and constructing heterojunctions during the growth process.Based on these flexible and excellent material properties,two-dimensional TMDs semiconductor materials have potential applications in nanophotonic and optoelectronic devices,such as light emitting devices,laser devices,light detectors,photovoltaic devices and optoelectronic logic devices.For the hotspot of two-dimensional TMDs,WS₂ with controllable growth layer and morphology was synthesized by chemical vapor deposition（CVD）.In this thesis the growth mechanism,material structure,optical and electrical properties of WS₂ were mainly studied.Secondly,the high quality two-dimensional layered WS₂ and the one-dimensional II-VI CdS nanowires were used to prepare the one-dimensional（1D）/two-dimensional（2D）hybrid heterojunction,and the application of the low-dimensional composite heterojunction in the direction of photoelectric detection was systematically explored.This thesis is expected to lay a foundation for the controllable preparation,structure characterization and device application of 2D WS₂ materials and their related heterojunctions.The concrete results obtained as follows:（1）Controllable preparation,morphology characterization and transistor characteristics of single-layer WS₂were studied.Firstly,WS₂ nanosheets with high quality and controllable layer number were prepared by CVD method,and the morphology,thickness and luminescence properties of the prepared materials were studied by optical microscopy,atomic force microscopy,photoluminescence and Raman spectroscopy.Secondly,the microstructure of WS₂ was characterized by scanning electron microscopy（SEM）and transmission electron microscopy（TEM）,and the results showed that the obtained material had high crystal quality and hexagonal lattice structure.Finally,by carefully modulating the growth parameters,the growth mechanism of WS₂ was studied in detail.（2）Controllable preparation and microstructure characterization of CdS/WS₂ 1D/2D heterojunction.Firstly,the CdS/WS₂ mixed dimensional heterojunction was prepared using WS₂ and CdS powder as original materials by a two-step CVD method by using WS₂ and CdS powder as original materials.Secondly,the epitaxial growth of CdS nanowires on the surface of WS₂ was proved by optical microscopy and SEM characterization,and the crystal orientation and composition of the two materials were further studied by X-ray diffraction（XRD）,ultraviolet photoelectron spectroscopy（XPS）and HRTEM.（3）Preparation and characterization of CdS/WS₂ heterojunction devices.CdS/WS₂heterojunction devices were fabricated by classical micro-nano machining method.The optical responsivity of the CdS/WS₂ heterojunction device is～50 A/W and the optical detection rate is～10¹²Jones.The optical responsivity and optical detection rate of the CdS/WS₂ heterojunction device can be 5472 A/W and 5×10¹³ Jones when the backgate voltage is added.Study on CdS/WS₂heterojunction light detector.It is proved that this heterostructure has potential application value in high efficiency optoelectronic devices.