Wafer-Scale Epitaxial Growth Of Monolayer And Bilayer Vertical Heterostructures Of Two-dimensional Semiconductors

Two-dimensional（2D）transition metal dichalcogenide has attracted much attention by science and industry for its excellent performance.The representative materials,such as 2D molybdenum disselenide（Mo Se₂）and molybdenum disulfide（Mo S₂）,are typical semiconductor materials and have great application potential in electronic devices and optoelectronic devices.Transition metal dichalcogenide can not only form atomic thin monolayers,but also form a variety of heterostructures by combinations of different materials,including lateral and vertical heterostructures with novel and adjustable physical properties,broadening the way for more research fields.To realize the application of these new 2D semiconductors,the effective preparation of large area and high quality monolayer films and heterostructures is an important research task.In this dissertation,we used the method of chemical vapor deposition（CVD）for wafer-scale 2D material growth and fabricated devices based on the CVD grown films,mainly including the following results:1.Epitaxial growth of 4-inch wafer-scale monolayer Mo Se₂ continuous films has been achieved.Using sapphire as the epitaxial growth substrate,the 4-inch wafer-scale Mo Se₂ films were obtained in a three-temperature zone CVD system by multi-source controlled growth method.The structural and spectroscopic characterization of the wafer-scale films proves to have good uniformity.The on/off ratio of Mo Se₂-based field-effect transistor（FET）devices is up to 10⁷.Moreover,the lateral heterostructures of Mo Se₂ was also successfully prepared by the CVD method.2.Epitaxial growth of 2-inch wafer-scale bilayer vertical heterostructures of TMDs has been achieved.The continuous films of 2-inch wafer-scale bilayer vertical heterostructures on sapphire substrates were obtained by a two-step CVD growth method.The heterostructure consists of two different monolayers with a clean interface.Bilayer vertical heterostructure films show good uniformity at large area.Devices based on the heterostructures have excellent optoelectronic properties and a response time up to tens of microseconds.3.Stretchable FET devices based on monolayer Mo S₂ films have been fabricated.The monolayer Mo S₂ film grown by CVD method is used as the channel material of the FET device.The stretchable Mo S₂FET devices were fabricated on elastic substrates by pre-stretch method.The device has a buckled structure so that it can withstand large strains,and can work stably and repeatedly before and after stretching.The stretchable Mo S₂FET devices were applied in optoelectronic synapses with high image recognition accuracy.