Theoretical And Experimental Study On Heterostructure Photoelectric Detector Of Bi₂Se₃ And TiO₂ Composite Thin Film

Topological insulators have only been known by people in recent years.As a hot semiconductor material in the field of condensed matter physics,it is different from general semiconductors in that it has surface conductivity and physical insulation.The conductive edge state passes through the Fermi surface and connects the bottom of the conduction band and the top of the valence band.The reason is the strong spin-orbit coupling effect protected by the time inversion symmetry in the material energy band.Take the topological insulator Bi₂Se₃as an example,it has a forbidden band width of about 0.3e V,and has a unique energy band structure and peculiar optical and electrical properties,and has strong light absorption for sunlight.Ti O₂material,as a typical photocatalyst,has good light stability and photosensitivity,and is widely used in solar cells,pollutant degradation,and photoelectric sensors.The effect of Bi₂Se₃and Ti O₂composite materials on solar cells is expected to increase the utilization rate of solar cells to sunlight.In this paper,the topological insulator Bi₂Se₃and Ti O₂are formed into a composite material by molecular beam epitaxy,which successfully extends the application of topological insulators to the field of photoelectric detection.This will greatly advance the application of topological insulators to real life.This paper first introduces the research status of topological insulators and their composite materials.The experiment uses molecular beam epitaxy to explore the experimental parameter conditions for growing high-quality topological insulators.And the use of different substrate materials such as Al₂O₃,In P and other epitaxial growth of high-quality topological insulator thin film;study the impact of different temperature conditions on the growth of topological insulator;A photoelectric detector was fabricated using the composite material of topological insulator Bi₂Se₃and Ti O₂,and the performance of the detector was analyzed.This article introduces in detail the use of semiconductor titanium dioxide（Ti O₂）as a substrate,the use of molecular beam epitaxy method to prepare high-quality topological insulator bismuth selenide（Bi₂Se₃）film,to form Bi₂Se₃/Ti O₂composite material.According to experiments,when epitaxial growth of topological insulator Bi₂Se₃thin film,the substrate temperature is set to 390℃,the Bi/Se flow ratio is controlled around 1:10,the growth time is 50minutes,and the thickness of the prepared film is about 50 nm.After the preparation is completed,the reflective high-energy electron diffractometer can be used to characterize the epitaxially grown Bi₂Se₃thin film samples in situ,to avoid the pollution caused by the samples in contact with the air to the greatest extent.The reflective high-energy electron diffractometer can see the clear and bright diffraction stripes of the sample,and the film surface is smooth and orderly.The crystal structure,surface morphology,optical and photoelectrochemical properties of the Bi₂Se₃/Ti O₂composite material were characterized by XRD,SEM,ultraviolet-visible near-infrared spectrophotometer and electrochemical workstation.The results show that the Ti O₂film modified by Bi₂Se₃still has a strong absorption peak in the visible-infrared region.Compared with the pure Ti O₂film,the absorption efficiency of sunlight is greatly improved.Subsequently,indium（In）electrodes and gold（Au）electrodes were vapor-deposited on Bi₂Se₃and Ti O₂,respectively,to make them into photovoltaic photodetectors,and then the light response characteristics and high-frequency response speed of the samples under different wavelength lasers were tested.