Effects Of La/Cu-doping And Point Defect On The Magnetic And Optical Properties Of ZnO By First-principle

ZnO is a II-VI direct bandgap compound,which has a wide bandgap,a high exciton binding energy,high temperature resistance and chemical stability.Its excellent performance is promising in semiconductor light emitting device,transparent conductive films,liquid crystal displays,varistors,gas sensors,and dilute magnetic semiconductors?DMSs?.ZnO-based DMSs have attracted increasing attention due to their unique spintronic properties and potential practical applications.Some achievements have been made in scientific research that doping of rare earth elements and transition metal elements can improve the physical properties of ZnO.However,the magnetic source of the rare earth element La and the transition element Cu doped ZnO is quite controversial,and the absorption spectra were red-shifted or blue-shifted of the La?Cu-doped ZnO is also controversial.Based on the above controversy,the effects of point defect on the magnetic and optical properties of La and Cu doped ZnO were investigated using geometry optimization and energy calculation on the basis of first-principles generalized gradient approximation+U?GGA+U?method of density functional theory.This papers use the CASTEP module.To solve the controversy about the magnetic source and mechanism of La-doped ZnO system,the electronic structures and magnetic properties of undoped ZnO,La-doped ZnO,and the systems with coexisting La doping and Zn or O vacancies were calculated.Results showed that the systems of La-doped ZnO and the coexistence of La doping and O vacancy were non-magnetic.In addition,the system of La replacing Zn and one Zn vacancy exhibits long-range orderly ferromagnetism,and the Curie temperature of the doping system can achieve room temperature.The magnetism source of the systems with La doping and Zn vacancy coexisting in ZnO demonstrates strong hybrid coupling electron exchange effects existing among Zn-4s,Zn-3p,O-2p,and La-5s orbits that are nearest to the Zn vacancy.The next nearest relative distance between doping and vacancy leads to the lowest formation energy and highest stability under the same doping condition.Compared with the pure ZnO system,the absorption spectrum of the La-doped ZnO system is blue-shifted.The experimental studies on Cu-doping and point defects lack focus on the magnetic and optical properties of ZnO.The emergence of first-principles can compensate for the experimental deficiencies.Different types of point defect doping were calculated using the first-principles.Results indicate that the band gaps of Zn₁₅CuO₁₆,Zn₁₄CuO₁₆,and Zn₁₅Cu_iO₁₆ systems are narrowed,whereas the absorption spectra are red-shifted compared with those of pure ZnO.In addition,the system with Cu replaces Zn,and Zn vacancy coexists in ZnO.The magnetic moment of the doping system is relatively the largest,the doping system can achieve a ferromagnetic long-range order,and the Curie temperature can achieve room temperature.As electron injection sources,this system can reach 100%electron spin-polarization and exhibit half-metallic properties,which is relatively favorable for the DMS.This system has certain theoretical reference value in the design and preparation of photocatalysts or DMS.