First-principles study of the electronic structure of Al and Sn co-doping ZnO system

sThe electronic structures of Zn1−x−yAlxSnyO (heavily doping: x=0, 0.06, y=0, 0.06; and lightly doping: x=0, 0.03, y=0, 0.03.) are investigated by using an ab initio pseudopotential method based on density functional calculations. To study the effects of doping concentration on the electronic structure, we have built two ZnO supercells with 32 atoms and 64 atoms. Structural calculations show that, due to the Al and Sn doping, ZnO lattice strains and lattice parameters change. Electronic structural calculations indicated that the energy band of impure ZnO moves toward the low-energy region attributed to the doping of Al and Sn. For different dopants and doping concentrations, the extent of the shift of energy band is different. For Al single-doped ZnO, with Al concentration increase from 3 at% to 6 at%, the shift decreases from 2.0 to 1.06 eV. For Sn single-doped ZnO, the shift increases from 1.83 to 3.57 eV, with Al concentration increase from 3 at% to 6 at%. However, the change of the Al and Sn co-doped samples is not obviously owing to the interaction between Al and Sn. On the other side, Al and Sn doping can induce the narrowing of band-gap. Compared with that of Al doping, Sn doping makes the band-gap narrowing more apparent. With the increase of Sn concentration, the band-gap reduces apparently (reduce is 3 at%:0.68, and 6 at%:0.80). However, the band-gap reduces slightly with Al concentration (reduce is 3 at%: 0.06, and 6 at%:0.29). For Al/Sn co-doping, the gap is in the middle of Al and Sn single doped ZnO. Therefore, the place of energy band and band-gap can be adjusted by Al and Sn co-doping.