Two-dimensional Group Ⅲ-Ⅵ Semiconductors: Controllable Synthesis And Optoelectronic Properties

In recent years,two-dimensional（2D）materials have attracted huge attention due to their unique physical and structural properties and their potential applications in optoelectronic devices,energy,and storage,etc.Group III-VI semiconductor 2D materials can be used to construct field-effect transistors（FET）,photodetectors,gas sensors and other devices because of their layer-dependent characteristics,wide range band-gap,diverse crystal structures and excellent optical,electrical and magnetic properties.At present,the most effective method for synthesizing 2D materials is chemical vapor deposition（CVD）,but there are still some problems during the preparation and device construction process:（1）There are various choices of growth substrates,but the construction of 2D material-based devices is often carried out on Si O₂/Si substrates,so device construction needs to go through a transfer process.However,the transfer process always causes damage and contamination to the material.Therefore,how to avoid damage to materials and achieve non-destructive construction of 2D material-based devices is the key point.（2）Non-layered 2D materials have a large specific surface area and are easily affected by the air environment.Moreover,the presence of a large number of unsaturated dangling bonds on the surface of non-layered 2D materials can serve as active sites for atomic adsorption in ambient air.Therefore,non-layered 2D materials are more susceptible to the influence of oxygen and water molecules in the air environment,thereby affecting the performance of the device.Therefore,the oxidation behavior of non-layered 2D materials is also an issue that needs to be studied at present.（3）The technology of synthesizing target 2D materials by CVD has been very mature,but the research on the controllable synthesis of 2D material size and thickness and its synthesis mechanism is not detailed enough.Therefore,exploring the effects of different growth process parameters on the material growth and analyzing its growth mechanism will help to realize the controllable preparation and device application of other 2D materials.In this thesis,the following research work is carried out based on the current problems:1.Since the transfer process can cause damage and contamination to the materials,we synthesizedγ-In₂Se₃nanosheets on Si O₂/Si substrates by CVD.In addition,the synthesizedγ-In₂Se₃has a single crystal with a hexagonal lattice structure and excellent crystal quality,and due to the inherent structural defects of the material,the constructedγ-In₂Se₃-based photodetector exhibits a stable broad spectral response from the near-ultraviolet to the near-infrared.Choosing Si O₂/Si as the substrate for the CVD method effectively avoids the transfer process,thereby avoiding its potential damage and contamination to the material,which is beneficial to improve the performance of the device.This strategy also provides a reference for the nondestructive construction of other 2D material-based devices.2.The oxidation behavior of 2D materials has a great influence on the performance of their devices,so we synthesized high-qualityβ-In₂S₃nanosheets by CVD and investigated their oxidation properties under ambient conditions.As the oxidation time increases,the sulfur vacancies are replaced by oxygen atoms,and an inner layer of In₂S_3-3xO_3xand an outer layer of In₂O₃are formed.The formed In₂S_3-3xO_3xcan act as a protective layer to prevent further oxidation.Due to the substitution of sulfur vacancies by oxygen atoms,the crystalline quality of the surface oxidation state is poor,and the responsivity of theβ-In₂S₃-based photodetector decreases but the response speed remains unchanged.On the other hand,theβ-In₂S₃-based FET repairs sulfur defects due to oxygen atoms,resulting in enhanced carrier mobility.3.Exploring the influencing factors and synthesis mechanism of the controllable synthesis of 2D materials by CVD will help to quickly realize the synthesis of target 2D materials.Therefore,we synthesized Ga Se with different morphologies by CVD,explored the effects of different growth condition on the morphology and structural properties of Ga Se,and briefly analyzed the growth mechanism.The synthesized Ga Se exhibits excellent nonlinear optical properties due to its non-centrosymmetric structure.Moreover,the constructed Ga Se nanosheet-based photodetector exhibits stable and fast photoresponse.This provides a reference for the controllable preparation of Ga Se and other 2D materials and their applications in optoelectronic devices.