The Preparation Of Bi₄Se₃ Film By Laser Molecular Beam Epitaxy And Its Structure Characterization And Dielectric Properties

Layered selenides（including Bi₂Se₃,Sb₂Se₃,In₂Se₃,et al）are semiconductor materials,because of their unique energy band structure and performance,have good development prospects,and have been widely used in optoelectronics and thermoelectricity.The traditional thermoelectric material Bi₂Se₃ has proved to be a three-dimensional strong topological insulator,and its special properties have attracted the attention of a large number of scholars.Recently,researchers have predicted through calculation analysis that Bi（111）film are two-dimensional topological insulators.The biatomic layer of Bi₂Se₃ and the biatomic layer of Bi form a layered（Bi₂Se₃）_m（Bi₂）_n series material by a certain stacking method.Therefore,the study of（Bi₂Se₃）_m（Bi₂）_n series materials is a very meaningful subject.The main research of this theory is the preparation and characterization of Bi₄Se₃film and the analysis of the physical properties of Bi₄Se₃ through the first principle study.Main tasks as follows:（1）Using laser molecular beam epitaxy（LMBE）equipment to prepare Bi₄Se₃film on sapphire（Al₂O₃）substrates,where appropriate parameters play a important role in the growth of films.In this paper,a large number of film samples are prepared by changing the temperature of the substrate and the energy of each laser.The Bi₄Se₃film was characterized by the RHEED,XRD,SEM,EDS and AFM,and the effect of different substrate temperature and the energy of the laser pluse on the quality of the thin film sample was analyzed.The results of the study indicate that the Bi₄Se₃ thin film sample can be obtained when the substrate temperature is 370℃and the laser energy is 150m J,the surface is smooth,the crystal quality is good,and composition close to ideal ratio.（2）The model of Bi₄Se₃was constructed using Materials Studio software.The first principle calculation is performed on the optimized Bi₄Se₃,and it is found that the Bi₄Se₃ flim is semimetallic.By analyzing the density of states and projected states,it is found that the P orbitals of Bi and Se atoms contribute greatly to the valence band near the Fermi level,rather than the contributions from the s orbitals.Dielectric performance analysis shows that the Bi₄Se₃ flim has the largest displacement polarization intensity at a frequency of 2.128×10¹⁴ Hz.The loss at low frequency is very small,and the electron loss reaches a maximum value at 4.1×10¹⁴Hz.The analysis of optical performance reveals that Bi₄Se₃ flim has high absorption rate in the ultraviolet band and can be used as ultraviolet electron detection materials.