First-principles Calculations Of Al/P Co-doped ZnO

The ZnO lattice parameters,the electronic structure,formation energy and Optical properties,including the intrinsic ZnO,Al,P doped system,ZnO(Al,P)system and ZnO(Al,P)system of zinc vacancies have been calculated by using Material Studio7.0 of density functional theory based on first-principles plane wave ultrasoft pseudopotential method and general gradient approximation.The results are as follows.Intrinsic ZnO material is a direct wide band gap semiconductor.After Al doping,the formation energy is small,the system is stable,the band gap decreases,the carrier concentration of the conduction band increases,which shows n-type.According to the Analysis of optical properties,the absorption peak is red shifted compared with ZnO.the reflectivity of the low energy region is slightly increased.In addition,PZn has lowest formation energy,which shows n-type among the P doped ZnO(PZn,PO,PZn-2VZn)system.After the vacancy of Zn,the formation,the band gap of the system increases,which is lower than that of the PO system.shows p-type.By comparing the results of Absorption spectra and the reflect spectra,which show the red shift degree and the reflectivity of the low energy region increase.on the whole,the formation energy of P doped ZnO is relatively high,and the band gap is larger,which is not conducive to p-type conductivity.Compared with the P doped system,the Al-P Co-doped system has lower formation energy,more stable structure.According to the band structures,the band gap decreases slightly,the bottom conduction band effective mass decrease and the conductivity increases,which shows n-type in the process of doping.for the Analysis of optical properties,such as the imaginary part of the dielectric function,absorption spectra,reflect spectra,the reflectivity and absorption increased in the low energy region.By comparing with Al-P,the Al-2P that has lower formation energy,smaller band gap,which is conductive to forming the higher conductivity system.Owing to the increasing of free electrons around P,which makes the overlap region of P,O increase.Furthermore,The covalent bond become more Stronger,the ionic bonds become more weak,which weakened repulsion between the free electron and electrical conductivity of the system.in addition,The imaginary part of the dielectric function,absorption rate and reflectivity in the low energy region are enhanced with the increasing of the concentration of P.Compared with the Al/P Co-doped system,with the increasing Zn Vacancies doping concentration,the formation of the doped system increases gradually,thus the stability weaken,and the band gap decreases first and then increases,presents p-type.in addition,the conductivity and formation energy can be improved for Al and P in a ratio of 1:2 co-dopingon the same condition further.furthermore,the results of charge density of difference and optical analysis indicate that the electron cloud overlapping become stronger with the increasing of zinc vacancy concentration.and led to the motion of shared electron.enhances the absorption in the visible and near ultraviolet regions.Make p-type become more obvious.As a result,the better p-type ZnO can be obtained by controlling the Al/P in the proportion of1:2 co-doing with zinc vacancy.