First-principles Calculations Of Electronic Structure And Optical Properties Of Doped ZnO

Due to forbidden band width of 3.37 eV,exciton binding energy of up to 60 meV,low dielectric constant,environmentally friendly,great optoelectronic performance and Piezoelectric properties,Wurtzite structure of ZnO,a new type II-VI oxide semiconductor material,is widely used in optoelectronic devices and has potential research value.In this paper,the intrinsic ZnO system,Mg and Cd single-doped and co-doped ZnO systems,Mg and Cd with different concentrations co-doped ZnO systems,and Cu and Cd single-doped and co-doped ZnO systems have been investigated by using the first principle plane wave pseudo-potential method based on density functional theory.Moreover,The properties of lattice parameters,electronic structure(including band structure,state density)and optical properties(including dielectric function,optical absorption spectrum,reflectivity and energy loss spectrum)of these systems have been discussed and analyzed theoretically.The research results are as follows:1.The volume of ZnO changes greatly with the single doping Cd,while Mg single doping has little effect on the volume of the system.In Mg/Cd co-doped ZnO,the structural stability of the system will be better because of the doping of Mg.In addition,Mg-doped ZnO can improve the light transmission performance of ZnO material in the high-energy region of the visible light region,and broadens the spectrum of ZnO material.Cd-doped ZnO will reduce the forbidden band width of ZnO System,and the absorption band edge of the system will have a significant red shift,and the absorption capacity and reflection of light in the visible region will decrease.It is also found that compared with Mg and Cd single doped ZnO,the light transmittance of Mg and Cd co-doped ZnO is higher.2.In the Mg and Cd with different concentrations co-doped ZnO,as the doping concentration of Cd increases,the volume of the system will be larger,but the system stability is better and the band gap value of the system is becoming more small,which shows that the band gap value range of ZnO materials can be well adjusted by controlling the concentrations of Cd in the Mg and Cd co-doped ZnO.It has a great reference significance for the controllable material aspects in the industry.Simultaneously,it is also found that in the Mg and Cd with different concentrations co-doped ZnO,the absorption edge of system appears obvious red shift,and the absorption and reflection of light in the high-energy region are weakened.Moreover,with the increase of the concentration of Cd,the decline in absorption and reflectance of the system in the high-energy region are more obvious.Combined with the law of conservation of energy,this indicates that the light transmission effect of the material is enhanced,which has a great application prospect in transparent materials,solar cells and UV laser devices.3.The carrier concentration and the conductivity of ZnO are improved,and the band gap value of the doping system is decreased in the Cu and Cd single doped ZnO.But,compared with the single doping of Cu or Cd,the crystal structure of the system is more stable,the band gap value is smaller,and the electrical conductivity of the material is better in the Cu and Cd co-doped ZnO.As for optical properties,the absorption edge of Cd doped ZnO system is red-shifted and the absorption coefficient decreases,while the absorption coefficient of Cu single doped ZnO system increases slightly in visible and ultraviolet waveband.However,in the Cu and Cd co-doped ZnO,the absorption and reflectivity functions decrease.Moreover,as the doping concentration of Cd increases,the band gap width of the system becomes smaller,and the absorption and reflection effects of the system decrease more significantly.Combined with the characteristics of Cu and Cd single doping,it indicates that in the Cu and Cd co-doped ZnO,different effects of light transmission performance will be exhibited by controlling the concentration of doped Cd.Therefore,controlling the ratio of Cu/Cd in the Cu and Cd co-doped ZnO can be used to make light-permeable materials with different efficiency.