Effects On Optical And Electrical Propertis For Ag Doped And Ag-N Codoped ZnO

ZnO is a new type II-VI compound semiconductor. It’s non-toxic and pollution-free, riches in raw materials with low production cost, and it has good thermal and chemical stability. ZnO has a large band gap and exciton binding energy. At room temperature, the direct band gap of ZnO is 3.37 eV, and its exciton binding energy is 60 meV. ZnO is transparent in the visible region with excellent luminescent properties at room temperature. Therefore, ZnO has vast applications in the production of liquid crystal displays, solar cells, gas sensors, UV laser diodes, transparent conductive films, and diluted magnetic semiconductors.Although good results on the effects of Ag doped and Ag-N codoped ZnO have been theoretically and experimentally achieved, however, there are still shortcomings in the researches. In order to solve the contradiction in the absorption spectrum for Ag-doped ZnO, according to the first-principles plane-wave pseudopotential of the spin-polarized density functional theory(DFT), the electronic structures and absorption spectra of ZnO were calculated using the method of generalized gradient approximation(GGA+U). The calculation results indicate that, with the mole fraction of impurity increases in a range from 0.0278 to 0.0417, the lattice constant, volume and total energy of Ag doped system increases, the doped systems become unstable; the formation energy increases, the doping becomes harder; the band gap of Ag doped system narrows, and the absorption spectra exhibits a redshift. The reason of contradiction in Ag-doped ZnO absorption spectrum was explained: it is not only caused by doped concentration but also the caused by difference in spatial scales of Ag doped ZnO thin film.In order to solve problem of Ag atoms and N atoms random occupying without considering the asymmetry of ZnO in the Ag-N codoped ZnO, the band structures and density of states for pure and Ag-N codoped Zn1-xAgxO1-xNx(x=0.03125, 0.0417 and 0.0625) in different orientations have been calculated based on the density functional theory with GGA+U method. The results show that, for the same doping concentration, the systems with Ag-N perpendicular to the c-axis is more stable than the systems with Ag-N along the c-axis, and doping more easy. For the same doping mode, as Ag-N codoped concentration increases, the doped systems become unstable and the doping becomes harder. Compared with the pure ZnO, the optical band gap of the systems with Ag-N perpendicular to the c-axis narrows. A red shift of absorption spectra for doped systems is observed. And as the Ag-N codoped concentration increase, the red shift of absorption spectra is more significant.In order to solve the contradiction in conductivity of Ag-N codoped Zn O, the band structures and density of states for Ag-N codoped Zn1-x AgxO1-xNx(x=0.03125, 0.0417 and 0.0625) systems with Ag-N perpendicular to the c-axis were calculated based on the density functional theory with GGA+U method. The results show that, as the Ag-N codoped concentration increase, the relative hole concentrations for doped systems increases, the hole effective mass in valence band maximum decreases, the hole mobility decreases, the ionization energy decreases, Bohr radius increases, the conductance increases, and the conductivity become better.Based on first-principle, the absorption spectrum and conductance for Ag doped and Ag-N codoped ZnO were calculated, and the lacks of relevant experimental studies were solved. It may be helpful to the design and preparation of the new optical and electrical materials using ZnO.