| The thermal stability of ZnO is the wurtzite structure, it is a kind of wide band gap(gap of 3.37 eV at room temperature) II-VI oxide direct band gap semiconductor material. Being a low dielectric constant, high electromechanical coupling coefficient,high exciton binding energy of 60 meV, high chemical stability and good optical,electrical and piezoelectric properties, ZnO has potential application value in many aspects. There were a lot of similarities between ZnO and GaN in the band structure.ZnO also has lower growth temperature, is considered to be a new generation of short wavelength optoelectronic materials and to be likely to replace GaN. In this paper, by using the first principles method, analysis of the electronic structure and optical properties of ZnO doped with different impurities. The main contents are presented as follows:Firstly, the electronic structure and optical properties of Ag doped ZnO are studied. In this paper, we adopt the density functional theory plane wave pseudopotential method to study the crystal structure, electronic structure and optical property for the different concentrations of Ag doped ZnO system. The results show that with the adoption of Ag, the lattice constants of the system increase gradually, the formation energy of the system becomes lower, the stability of the system becomes stronger, Fermi level enters into the valence band, make the system show p-type conductivity, at the same time we found that the forbidden band gap of the Ag doping system is smaller. On the other hand, certain changes of the optical properties of Ag doped ZnO have taken place, moreover, the doping of Ag not only causes the absorption wave length to red-shift, but also leads to the emergence of a new strong peak at the place of 0.199 ev in the dielectric function.Secondly, the electronic structure and optical properties of S doped ZnO are studied. In this paper, we adopt the density functional theory plane wave pseudopotential method to study the crystal structure, electronic structure and optical property for the different concentrations of S doped ZnO system. The results show that with the adoption of S, the lattice constants of the system increase gradually, the formation energy of the system becomes lower, the stability of the system becomes stronger, the forbidden band gap of the S doping system is smaller. On the other hand,certain changes of the optical properties of S doped ZnO have taken place, moreover,the doping of S not only causes the absorption wave length to red-shift, but also leadsto the emergence of a new peak at the place of 2.66 ev in the dielectric function, the peaks of dielectric function become large at the same time shift to lower energy.Finally, we studied the optical and electrical properties of Ag-S co-doped ZnO.The results showed: compared with the eigen structure of ZnO, the energy band of various proportions of Ag, S co-doped ZnO shift to lower energy and the energy gap is widened. Through comparative analysis, we found that the formation energy of Ag-2S co-doped ZnO is the lowest, which shows the doping system is the easiest to form. On the other hand, compared with various proportions of Ag, S co-doped ZnO,we found that the forbidden band gap of Ag-2S co-doped ZnO becomes small, there is a shallow acceptor state appearing near the Fermi energy and the system exhibits some p type electrical conductivity, but it is not enough obvious. Through studied the system of 2Ag-S co-doped ZnO, we found that the forbidden band gap of 2Ag-S co-doped ZnO becomes smaller, there are more acceptor state appearing near the Fermi energy, more density of states near the Fermi level enters into the surface of Fermi energy, provide more carrier-holes, showed evident p type electrical conductivity. On the other hand, after 2Ag-S co-doped ZnO, certain changes of the optical properties of the system have taken place, moreover, the doping of 2Ag-S not only causes the absorption wave length to red-shift, but also leads to the emergence of a new peak in the region of 16.48-18.73 eV, at the same time, there is a big strong peak appears in the dielectric function at 0.994 eV, the other peaks of dielectric function become small at the same time shift to lower energy. |
