Study On The Growth And Interface Effects Of Two-Dimensional Sulfur(Selenium) Compund Semiconducter Materials

Two-dimensional(2D)materials have important applications in microelectronics,energy and catalysis due to their unique physical and chemical properties.In this paper,several 2D transitional metal sulfides(selenides)are prepared by improving the traditional method of chemical vapor deposition and mechanical exfoliation.We investigate the applications of these materials in photodetector and gas sensor,and explore the interface effects of 2D semiconductor and high-power function metals.The thesis is structured as below:In Chapter 1,we introduce the structure,types and research progress of 2D materials,including the characteristics and research progress of several common 2D materials;Preparation,transfer method and application of 2D materials and heterojunctions;Principles and uses of three common devices for surface topography analysis and structural characterization.In Chapter 2,we analyze the factors influencing the growth of MoS2 by chemical vapor deposition(CVD).We reveal the complete evolution of MoS2 from wafers,approximate wafers,hexagons,truncated triangles,triangles,indented triangles to tridents as the relative concentration of Mo source decreases.Based on molecular dynamics,the CVD growth process of MoS2 is optimized,and large size monolayer MoS2 with clean surface is obtained.The electrical characteristics and photoelectric detection ability of MoS2 are studied.This work provides a valuable reference for the research of CVD growth and physical properties of MoS2 and other 2D materials.In Chapter 3,we test the following devices:PtTe2-MoS2,Au-MoS2 and Cr-MoS2 by constructing PtTe2(transfer),Au(steam plating)and Cr(steam plating)electrodes.The interface effects between MoS2 and high work function metals are studied.There is no cutoff state in the three devices under the reverse gate voltage of-80 V.The calculation shows that the MoS2 crystal is a heavily doped n-type semiconductor.The Schottky diode formed by the interfactional contact of PtTe2 and MoS2 atomically has a very low reverse current,and the rectification ratio is as high as 104,nearly three orders of magnitude higher than the Au-deposited device.In addition,it is found that the intermediate state devices are prone to generate tunneling current,indicating that higher semiconductor doping concentration greatly increases the possibility of electron tunneling from metal to semiconductor under larger reverse bias.In Chapter 4,the transition temperature zone is set in the traditional CVD process,which can effectively reduce the deposition temperature of SnSe2,and the centimetersize SnSe2 polycrystalline film is directly grown on the flexible polydimethylsiloxane(PDMS)substrate.The results of X-ray diffraction and Raman spectroscopy show that SnSe2 films are of high quality.After a thousand bends,the SnSe2 film does not crack or separate from the substrate,and the Raman spectra of the film does not change significantly.In addition,a flexible SnSe2 gas sensor is fabricated.At room temperature(27℃),the response of the gas sensor to 6 ppm NO2 is 200%,the response time is 105 seconds,and the recovery time is 230 seconds.High efficiency at room temperature and flexibility make it promising for gas sensor,such as NO2 and NH3,and provide a new solution for the next generation of flexible wearable electronic devices.In Chapter 5,we report an efficient and transfer-friendly polyvinyl alcohol(PVA)assisted stripping scheme for van der Waals materials.Using the characteristics of smooth and good viscosity of PVA layer at high temperature,centimeter-scale graphite sheets and hundred-micron ZnIn2S4 and BN samples are obtained by peeling.It is found that the number of BN stripped by PVA is 8 times higher than that of the ordinary SiO2/Si substrate,and the samples sizes are also significantly increased.Since PVA is easily soluble in water,the stripped material can be transferred to a new substrate by soaking it in deionized water.Raman and X-ray photoelectron spectroscopy of the graphite sheets show that the stripping and transfer processes are gentle to the samples.In addition,PVA can be used as a gate dielectric,and electronic devices can be made directly from PVA-assisted stripped samples.Chapter 6 is the summary and prospect.