Effects on the optical properties and conductivity of Ag-N co-doped ZnO

Nowadays, the studies of the effects on the optical bandgap, absorption spectrum, and electrical properties of Ag-N co-doped ZnO have been extensively investigated. However, Ag and N atoms in doped systems are randomly doped, and the asymmetric structure of ZnO is yet to be explored. In this paper, the geometric structure, stability, density of states, absorption spectra and conductivity of pure and Ag N co-doped (x= 0.03125,0.0417 and 0.0625) in different orientations are calculated by using plane-wave ultrasoft pseudopotential on the basis of density functional theory with GGA+U method. Results show that the volume, equivalent total energy and formation energy of the doped system increase as the concentration of Ag-N co doped Zn1-xAgxO1-xNx increases at the same doping mode. The doped systems also become unstable, and difficulty in doping. At the same concentration of Ag N co-doped Zn1-xAgxO1-xNx, the systems with Ag N along the c-axis orientation is unstable, and doping is difficult. The optical bandgap of Ag N co-doped systems is narrower than that of the pure ZnO. At the same doping mode, the optical bandgap of the systems with Ag N perpendicular to the c-axis orientation becomes narrow as the concentration of Ag-N co-doped Zn1-xAgxO1-xNx increases. The absorption spectra of the doped systems exhibit a red shift, and this red shift becomes increasingly significant as the concentration of Ag-N co-doped Zn1-xAgxO1-xNx increases. Under the same condition, the relative hole concentrations of the 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. Our results may be used as a basis for the designing and preparation of new optical and electrical materials for Ag-N co-doped ZnO applied in low temperature end of temperature difference battery.