Preparation And Optoelectronic Properties Of Metal Chalcogenide Semiconductor Micro/nano Structures

Due to the unique properties,two-dimensional materials have shown considerable potential in various fields.After the exploration of researchers in recent years,the two-dimensional material heterojunction which can combine the advantages of various materials and bring the unique interface characteristics of the heterointerface,furt her promotes the research of two-dimensional material devices.The transition metal dichalcogenide（TMDs）family of materials has various variety such as semiconductors,（semi）metals,and topological insulators.Among them,TMDs semiconductors have different physical properties such as band gap,electron affinity and light absorption coefficient.The variety of materials brings a wid e range of applications to TMDs and is also very suitable for constructing 2D heterojunctions for different fields.In order to study the methods to improve the electronic and optoelectronic device performance of two-dimensional materials,this thesis takes two-dimensional heterojunctions as the main research object.The metal-semiconductor heterojunctions and the semiconductor heterojunctions were prepared by a two-step chemical vapor deposition method,respectively.The main research results are as follows:A high-quality NiTe₂/WS₂ metal-semiconductor vertical heterojunction was successfully fabricated with two-step CVD,and the optical and microscopic characterization results showed that the metal-semiconductor heterojunction had high crystal and interface quality.In order to obviously show the performance difference between NiTe₂/WS₂ heterojunction devices and pure WS 2 devices,we fabricated back-gate FET devices based on NiTe₂/WS₂ and pure WS₂ based on the same heterojunction,respectively.The source-drain electrodes are fabricated on the two sheets of NiTe₂ in the heterojunction while the electrodes of the pure WS ₂device are fabricated directly on the underlying WS₂.After the same growth and preparation process,the pure WS 2devices exhibit n-type FET characteristics,while heterojunction devices transform into p-type FET characteristics and have a higher 4.22 cm²/V·s hole mobility,which can be attributed to the damage to the metal-semiconductor interface caused by the traditional electrode process,resulting in the Fermi level pinning effect,while the van der Waals metal-semiconductor interface with heterojunction forms an ideal Schottky junction,got a lower hole barrier;in a number of tests of photodetection,the excellent van der Waals metal-semiconductor contact enables the performance of heterojunction devices to be improved by dozens of times.In order to study WS₂-based semiconductor-semiconductor heterojunction optoelectronic devices,we fabricated Sn Se/WS ₂ semiconductor heterojunctions by the same two-step CVD method,and the preliminary optical and Raman mapping showed that the heterojunction has a high quality.Sn Se and WS ₂ form a type II energy band,and the photo-generated electron-hole pairs at the heterojunction are separated into WS₂ and Sn Se.According to this characteristic,we design the structure of the optoelectronic device.In this paper,we demonstrate through NiTe₂/WS₂ heterojunction that a good metal-semiconductor contact can be prepared by CVD method,which can significantly improve the optoelectronic properties of the device,and the appropriate energy band structure can also bring about a change in the polarity of the FET,provided a approach to improve the performance of 2D materials-based devices and to control the polarity of FETs.