First-principles Study On The Half-metallic Properties Of Cr,Mn Doped AlN And GaN

Spintronics, at the cross of magnetism, electronics and informatics, is a new emerging field of research in considerable expansion. It can use both electronic charge and spin for information storage and processing. The advantages of the spintronic devices would be nonvolatility, increased data processing speed, decreased electric power consumption and increased integration densities compared with conventional semiconductor electronic devices. At present one of the key problems is to find the spintronic materials with high rate of spin polarization and high Curie temperature. As AlN and GaN are wide band-gap semiconductors, transition metals (Cr and Mn, etc.) doped AlN and GaN can be half-metallic materials with high Curie temperature and high rate of spin polarization (100%). Therefore, AlN and GaN based Diluted Magnetic semiconductors (half metal) would have important application value in the field of spintronics.In this paper, by using the first principles method which base on density functional theory (DFT), we calculated the energy band structures and density of states of Cr and Mn substitutional doped wurtzite and zincblende of AlN and GaN. Through systematically studying the half-metallic magnetic mechanism of Cr and Mn doped AlN and GaN, and analyzing the doped concentration's effect on the half-metallic gap, We come to the following major conclusions:(1) Cr(Mn)-AlN have relatively wide half-metallic gaps, and the half-metallic gaps of Cr(Mn)-GaN are relatively smaller. The main cause is that the semiconductor band gap of GaN is smaller than AlN, and the down-spin bands of Cr(Mn)-GaN are strongly influenced by Ga-4s and Ga-4p orbital and broaden to the Feimi level, thus the half-metallic gaps of Cr(Mn)-GaN are smaller than Cr(Mn)-AlN.(2) With the same doped concentration, the half-metallic gaps of Mn-Al(Ga)N are larger than Cr-Al(Ga)N. This is because the Mn-d states are lower than Cr-d states, and the p-d hybridization is stronger in Mn-Al(Ga)N, which results in the spin-exchange splitting is larger, so the down-spin bands of Mn-Al(Ga)N move far away from the Feimi level, and the half-metallic gap turns larger.(3) For wurtzite and zincblende Cr(Mn)-AlN, Cr(Mn)-3d states play a decisive role in the conduction band minimum of down-spin bands, that is, the half-metallic gap is determined by Cr(Mn)-3d states. Within the doped concentration range of 6.25% to 25%, the half-metallic gap decreases with increasing the Cr(Mn) doped concentration: The half-metallic gaps of wurtzite Mn-AlN decrease from 1.49eV to 0.95eV, the half-metallic gaps of zincblende Mn-AlN decrease from 1.56eV to 1.08eV, the half-metallic gaps of wurtzite Cr-AlN decrease from 1.13eV to 0.79 eV, and the half-metallic gaps of zincblende Cr-AlN decrease from 0.69eV to 0.56eV. The main cause is that the interaction between Cr(Mn) atoms enhances with increasing the Cr(Mn) doped concentration, and the Cr(Mn)-3d bands widen to both sides, which results in the decrease of the conduction band minimum of down-spin bands, so the half-metallic gap reduces. However, for wurtzite and zincblende Cr(Mn)-GaN, the down-spin bands which decide the half-metallic gap are mainly from the hybridization of Cr-3d and N-2p states, and at the same time, it's influenced by Ga-4s and Ga-4p orbital. With the doped concentration increasing, the interaction between Cr(Mn) atoms'effect on the half-metallic gap is not significant. so the half-metallic gaps of Cr(Mn)-GaN are relatively steady with increasing the doped concentration. Within the doped concentration range of 6.25% to 25%, the half-metallic gaps of wurtzite Mn-GaN are between 0.85~0.71eV, the half-metallic gaps of zincblende Mn-GaN are between 0.74~0.65eV, and the half-metallic gaps of wurtzite and zincblende Cr-GaN are 0.2eV aroud. All of them have little relationship with the doped concentration.Our calculation results agree well with the existed research results. It proves that our calculation method is reliable and feasible. In addition, some new results and new laws are obtained, and we try to explain them. Although they still need to be verified by theories or experiments, we belive that they are definitely helpful on the further study of the property and application of AlN and GaN based diluted magnetic semiconductor (half metal).