Study On The Physical Properties Of Mo/Ce Doped ZnO By First Principle

ZnO has perfect crystal properties,good stability under high voltage and high temperature,and is a wide bandgap semiconductor material.With excellent physical properties,ZnO has great application value in the fields of transparent conductive oxides,photocatalysts,optoelectronic devices,and dilute magnetic semiconductors.A large number of theoretical and experimental studies have demonstrated that doping of transition metal elements and rare earth elements can improve the physical properties of ZnO.Therefore,in the range of 2.08-3.13at.%of Mo doping concentration,there existed two experimental results of red-shift and blue-shift of absorption spectrum.At the same time,the absorption spectrum and magnetic mechanism of ZnO doped with rare earth element Ce are controversial.In order to solve these problems,this paper uses the CASTEP module in Materials Studio 8.0.The optical,electrical and magnetic properties of transition metal Mo and rare earth element Ce doped ZnO were calculated based on the first-principle-generalized gradient approximation+U（GGA+U）method of density functional theory.To resolve the divergence of the absorption spectra of Mo doped ZnO system,ZnO,Zn_0.9583Mo_0.0417O and Zn_0.9375Mo_0.0625O systems are constructed by first-principals.In addition,in order to study the magnetism of the doping systems,three kinds of Zn₁₄Mo₂O systems with different spacing positions were constructed.The result indicates that,with the increases of Mo-doping concentration in a range from 0.0208 to 0.0313,the volume and the formation energy increase while the stability of the doped system decreases,and the Mo-doping becomes more difficult.At the same time,the more Mo doping content is,with all the doping systems converted into n-type degenerate semiconductor.Compared with pure ZnO,the energy band gaps of the doping systems become narrower,this paper reasonably explained the mechanism of band gap narrowed,and the absorption spectra is occurred red shift.Therefore,the results further confirmed that Mo doped ZnO is a candidate photocatalyst for potential applications.With the increase of Mo doping concentration,the energy band gap of the doping system becomes wider,which reveals that the red shift of absorption spectra becomes weaker.The carrier concentration,mobility and conductivity are calculated as well.The calculated results show that,with the increases of Mo-doping concentration,carrier concentration,mobility and conductivity of the doping systems decrease.The calculation results of energy band gap,absorption spectra and conductivity of Mo doped ZnO systems are consistent with the experimental data.Simultaneously,these results may contribute to improve the design and the preparation of photoelectric functional materials for Mo doped ZnO at quite a low temperature.Noticeably,this finding revealed that the double-doped systems possess high Curie temperature and achieve room temperature ferromagnetism.Therefore,Mo doped ZnO can be practically used as an unambiguous diluted magnetic semiconductor,and with the increase of the doping concentration,the magnetic moment decreases.To solve the controversy over Ce-doped ZnO absorption spectrum and magnetic mechanism,we established a unit cell of undoped ZnO and supercell models of Ce mono-doped ZnO at different concentrations and Ce-double-doped ZnO at various spatial arrangements.We calculated the electronic structure and optical properties of Ce mono-doped ZnO systems.We also determined the relative energy of ferromagnetic（FM）and anti-ferromagnetic（AFM）orders of Ce-double-doped ZnO systems.Results indicated that higher Ce doping amount of Ce-mono-doped ZnO systems results in higher doping system volume,higher formation energy and lower system stability.The band gaps of Zn_1-xCe_x O（x=0,0.0313,0.0417,and 0.0625）are 3.40,2.98,3.12,and 3.19 eV,respectively.And the absorption spectrum is red-shifted for mono-doped systems.Ferromagnetism is mainly attributed to the hybrid coupling effect of Ce-4f,Ce-5d,and O-2p states.The calculated magnetic moments of mono-doped systems respectively reached 0.965,1.012,and 1.014?_B.The ferromagnetism of mono-doped systems increases as the Ce doping concentration increases.A relatively stable anti-ferromagnetic state is observed when-Ce-O-Ce-doped in a direction along the a-axis bonding of the Ce double-doped ZnO system,whereas a favorable ferromagnetic state is found when-Ce-O-Ce-doped in a direction along the deflection of the c-axis.This finding revealed that the double-doped systems possess high Curie temperature and achieve room temperature ferromagnetism.Through the first-principles,we obtained the effect of Mo doping concentration on the conductivity of ZnO,solved the differences in the absorption spectra of Mo or Ce doped ZnO systems,and found room temperature ferromagnetism of Mo,Ce doped ZnO systems.Moreover,the magnetic mechanism of the doping system is reasonably explained from the microscopic point of view,which has theoretical guiding significance for the design and preparation of ZnO photocatalysts and diluted magnetic semiconductor.