The Electronic Structure and Optical Properties of Al-N Codoped ZnO

The electronic structures and optical properties of pure and Al-N codoped wurtzite ZnO were calculated using first principle ultrasoft pseudopotential approach of the plane wave based upon the density funcational theory.Codoped theory showed that,in the ZnO doped system,when the concentration of Al and N equal,Al-N complex formed,N may be fully compensated,but the concentration of N is twice or more times as the concentration of Al,may be the formation of Al-N2,Al-N3,Al-N4 complex,these complexes are likely to reduce the ionization energy of a single N atom.To verify the feasibility of this approach,we chosen 32-atom supercell model to calculated the electronic structure and related parameters of the Al-N codoped wurtzite ZnO,and analysised the mechanism of the increasing of the hole concentration in Al-N codoped p-type ZnO.Firstly,we calculated the binding energy of Al-N complex codoped ZnO and found that Al-N complex can exist in ZnO stably,therefore Al-N codoped ZnO can improve the N solubility of doping.Studies showed that,due to the orbital hybrid between N-2p and Zn-3d,the Fermi level is deeply into the valence band,the top of the valence band shift up and the bottom of the conduction band shift down,resulting in the band gap narrowed.While proper control the ratio of Al and N,the exclusion between the acceptor atoms weakened and the acceptor level was lower after the Al-N complex doped ZnO.So Al-N codoping is an important method to improve the characteristic of p-type ZnO.Besides,in the Al-N codoped ZnO system,the decrease of band gap and the absorption bandedge red-shift will happen after Al-N codoping,experimental phenomena also approve the result.