Impurity Effects On The Optical, Electronic And Magnetic Properties Of Two-Dimensional Arsenene And C₂N Materials

Since the successful exfoliation of graphene in experiment,two-dimensional materials have attracted extensive attention because of their novel optical,electronic,and magnetic properties.They have also been widely applied in optoelectronic and nanoelectronic devices,such as solar cells,luminescent device,field effect transistor and so on.However,there are still some problems in the practical application of two-dimensional materials,such as the effect of doping on the stability and optoelectronic properties of two-dimensional materials.Therefore,in this thesis,we have studied the effect of doping on the electronic,magnetic and optical properties of Arsenene and C₂N nanosheets using the first-principles calculation method based on the density functional theory?DFT?.Mainly results are given as follows.Firstly,group IV and VI dopants can effectively tune the electronic structures of arsenene.The results show that for group IV atom?C,Si,Ge and Sn?-doped arsenene nanosheets,they all exhibit the magnetic ground states.Group IV doping can induce deep acceptor impurities,which imply that group IV atoms substituting As atom are not suitable for achieving p-type conductivity in the arsenene.However,for the group VI atoms?O,S,Se and Te?-doped arsenene,they all exhibit the non-magnetic ground states?except O?,the defect states of O impurity lie in the middle of the band gap,which indicates that O impurity can not induce effective n-type carriers in the arsenene.Moreover,the results also show that Te atom doping is the most effective n-type doping due to the shallowest transition energy level in the arsenene.In addition,the formation energy and transition energy levels depend highly on the atomic size of impurity atom for all the doped systems.This dependence indicates that suitable atomic size plays an important role on the feasibility of doping in arsenene in experiments.Secondly,the modification of electronic structures and magnetic properties of arsenene by 3d TM atoms doping.The calculations show that Sc-and Co-doped arsenene cases retain the nonmagnetic semiconductor characteristic,while Ti-,Cr-,and Cu-doped arsenene exhibit the properties of dilute magnetic semiconductor.Moreover,V-,Mn-,Fe-,and Ni-doped arsenene systems posses the half-metallic properties,and Zn-doped arsenene presents the metallic states.More interestingly,under their most stable configuration,the magnetic coupling between magnetic moments induced by Ti,V,Mn,and Fe are found to be FM.In contrast,an AFM coupling occurs between the magnetic moments induced by Cr.In general,our theoretical calculations suggest that the electronic structures and magnetism can be tuned effectively in the2D arsenene nanosheets.Thirdly,the modification of structural,electronic and magnetic properties of C₂N monolayer via 3d TM atoms embedding.The results show that Sc,Ti,V,Cr,Fe,Ni,Cu and Zn atoms can be stably embedded in the porous C₂N monolayer.The magnetic moments of the 3d TM-embedded porous C₂N monolayer show an increasing tendency when the atomic number increases for the early TM atoms,while a decreasing tendency is presented with the increasing atomic number for the late TM atoms.The maximum magnetic moment can be reached in the Mn-embedded porous C₂N monolayer,while the minimum magnetic moment is obtained in the Zn atom-embedded case.Moreover,numerical results also show that Sc,Ti,V,Cr,Mn,Fe,Co and Ni atom-embedded cases possess ferromagnetic states,while embedding the Cu atom can induce paramagnetic characteristics in the porous C₂N monolayer.Meanwhile,the Zn-embedded C₂N monolayer exhibits a nonmagnetic ground state.Finally,the regulation of electronic and optical properties of C₂N monolayer by isovalent atoms doping.The results show that the cohesive energies show a decreasing trend with the increasing doping concentration and atomic number of the doping atom in the period table,and the cohesive energies of C₂N_1-xA_x alloys are higher than that of C_2-xB_xN alloys with the same concentration.Moreover,both the band gap and the threshold energy values of C₂N_1-xP_x and C₂N_1-x-x As_x alloys decrease monotonically with the increase of doping concentration,while the values of the static dielectric constants?₁?0?are increased.In addition,the absorption edges of the C₂N_1-xP_x and C₂N_1-xAs_x alloys exhibit a red shift with respect to pristine C₂N.These results are interesting and useful to understand the electronic structures and optical properties of C₂N_1-xP_x and C₂N_1-xAs_x alloys.However,experimental studies for the C₂N_1-xP_x and C₂N_1-xAs_x alloys are still lacking at present.