First-principles Study Of The As₂S₃

Arsenic chalcogenide layered materials are widely used in electronic devices,sensors and energy systems due to their low symmetry and high anisotropy.P2₁/c-As₂S₃,P（?）-As₂S₃and P2₁/c-As₂Se₃ has excellent chemical stability and photoelectric properties.Therefore,the photoelectric and mechanical properties of P2₁/c-As₂S₃,P（?）-As₂S₃ and P2₁/c-As₂Se₃ are compared and analyzed.The crystal doping will play a key role in the optical,electrical and magnetic properties of the system.The physical properties of P2₁/c-As₂S₃ can be regulated by using transition metal substitution doping and introducing vacancy defects,and its application range in optoelectronic devices and other fields can be expanded.Based on density functional theory（DFT）,the basic physical properties of P2₁/c-As₂S₃,P（?）-As₂S₃and P2₁/c-As₂Se₃ are studied under van der Waals correction（DFT-D3）.At the same time,the performance of P2₁/c-As₂S₃ regulated by transition metal substitution doping and vacancy defects is calculated.The specific research work is as follows:1.The lattice constants of P2₁/c-As₂S₃,P（?）-As₂S₃and P2₁/c-As₂Se₃ are obtained by relaxation,which are in agreement with the theoretical experimental results.The band gap values of the three structures are calculated by Perdew-Burke-Ernzerhof（PBE）and HSE06hybrid functional.The band gap values obtained by the former are in good agreement with the theoretical literature values,and the band gap values obtained by the latter are closer to the experimental results.The elastic constants(C_ij)of single crystals are calculated by energy-strain（E-S）method and stress-strain（S-S）method for the three structures after relaxation,which all met the criteria of mechanical stability.The polycrystalline elastic modulus and anisotropy factor of the three structures are calculated by C_ij obtained by S-S method.The three-dimensional characterization of Young’s modulus（E）and linear compression coefficient（β）shows the strong anisotropy of P2₁/c-As₂S₃,P（?）-As₂S₃and P2₁/c-As₂Se₃ crystals.In addition,the optical properties of the three structures are calculated,including dielectric function,absorption coefficient,refractive index,reflectivity,extinction coefficient and loss function.The results show that P2₁/c-As₂S₃ and P（?）-As₂S₃ have high transparency in the infrared region,P2₁/c-As₂Se₃ is most suitable for ultraviolet light reflection,and the three structures have strong absorption in the visible region.2.The effects of substitutional doping of transition metals（Mn,Fe）and the introduction of vacancy defects on the system were studied.Through the analysis of formation energy,it is concluded that As_2-xMn_xS₃（x = 0.0625,0.125,0.25）systems are spontaneously formed;in the As_2-xFe_xS₃（x = 0.0625,0.125,0.25）system,the formation energy of As_1.75Fe_0.25S₃ is the lowest.Therefore,the mechanical analysis of As_1.75Mn_0.25S₃ and As_1.75Fe_0.25S₃ is carried out,it shows that it satisfies mechanical stability.The analysis of As_2-xTM_xS₃（TM=Mn,Fe;x=0.0625,0.125,0.25）system by Bader charge and differential charge diagram shows that the electronegativity of iron（Fe）in the system is greater than that of manganese（Mn）.Due to the influence of impurities,the compounds are magnetic,of which As_1.75Mn_0.25S₃ is a magnetic half-metal,and the rest of the system is a magnetic semiconductor.In the As_2-xTM_xS₃（TM=Mn,Fe;x=0.0625,0.125,0.25）system,the contribution of the magnetic moment is mainly provided by the TM impurity,and the magnetic moment of the As_2-xMn_xS₃（TM=Mn,Fe;x=0.0625,0.125,0.25）system is the largest.The atomic magnetic moment of Mn has a significant effect on the total magnetic moment of the system.Through the analysis of the dielectric function,it is found that the imaginary part of the dielectric function shows a new peak in the infrared region with the increase of the doping concentration,which is mainly caused by the electron transition,indicating that the dielectric loss increases.The calculation results of the optical absorption coefficient show that the absorption range of the system has different degrees of red shift,which expands the light absorption range,which is beneficial to the application of optoelectronic devices.