| Two-dimensional materials have attracted great attention owing to unique physical and chemical properties due to their abundant elemental compositions and special electronic structures,which have great potential in the fields of optics and electronic devices.In this article,the research goal is to expand the research boundary of two-dimensional semiconductors,explore new functions,new application scenarios and use new strategies to synthesize large-size and high-density devices of two-dimensional semiconductor materials.We have carried out three tasks based on three materials:ZnIn2S4,SnSe2 and WSe2,in combination with the technology we have and the materials we have obtained.The main body of the paper is divided into five chapters as follow:In chapter 1,we briefly introduce the development of two-dimensional materials,the acquisition methods of ultra-thin materials,the research status of two-dimensional material devices and optoelectronic devices.Then We propose the basis for selecting the topic of the thesis and briefly introduce the research content.In chapter 2,with the goal of expanding the range of two-dimensional semiconductors,we discovered a new type of two-dimensional semiconductor ZnIn2S4 and studied its electrical properties.ZnIn2S4 single crystal was synthesized by chemical vapor transport.And ZnIn2S4 with different thicknesses were obtained by mechanical exfoliation method.The experiment demonstrates an attractive thickness-dependent direct bandgap of about 2 eV.ZnIn2S4 also exhibits excellent air stability and good optoelectronic performance.The off-state current of ZnIn2S4 is as low as 4×10-12 A,which is quite low among currently known two-dimensional materials.ZnIn2S4 is expected to become the material of choice for the manufacture of next-generation low-power devices.In chapter 3,to expand the flexible application environment of two-dimensional semiconductor materials as the research goal,large-size SnSe2 flexible thin film devices were prepared and its photoelectric performance were studied.Using low-melting raw materials and new growth strategies,the polycrystalline SnSe2 film was successfully grown on the flexible organic silicon(PDMS)substrate.The optical properties of the sample underwent multiple folds or stretched and bent of varying degrees remain unchanged.Tested with LED lasers of different wavelengths,it is found that SnSe2 film have obvious photoelectric response.The SnSe2 film is most sensitive to 532 nm light,with response time of less than 40 ms.The device based on SnSe2 film still maintains good optoelectronic properties under high strain.and Under the test conditions of incident laser wavelength of 532 nm,power of 20.6 mW,and bias voltage of 5 V,the device with a curvature of 12%still has photoresponsivity of 724 mA W-1 and detectivity of 2×109 Jones.Compared with typical flexible devices such as WS2/PI,MoS2/PEN and WSe2/PI,the performance of SnSe2 flexible devices is excellent.In chapter 4,with the goal of selecting excellent semiconductor materials,improving experimental methods to obtain large-size films,and manufacturing high-density devices,the synthesis and transfer of WSe2 are studied.By selecting different tungsten sources and pre-processing the sources,optimizing various growth parameters,the millimeter-size WSe2 was successfully synthesized by a salt-free method at first time.The sample was verified to be an uniform monolayer film by analyzing the optical microscopy,Raman and PL data at different positions.The millimeter-size monolayer WSe2 was successfully and efficiently transferred by Using BOE as the etching solution.It provides a material basis for the subsequent research and application of high-density devices.In chapter 5,the summary and the prospect.During the PhD.degree,we also conducted a critical analysis of the single crystal La0.67Ba0.33MnO3(LBMO)film.The experimental results show that the critical behavior in the LBMO film is close to the 3D Heisenberg model.The content of this part is in the appendix of the article. |
PDF Full Text Request