Conversion of n-type to p-type conductivity in ZnO by incorporation of Ag and Ag-Li

Elemental doping is an efficient strategy to modulate different properties of semiconductors. Conversion from n-type to p-type and band gap modulation of ZnO are investigated by theoretical and experimental pathways studies. The structural, electronic and optical properties of undoped, Ag and Ag-Li doped ZnO are studied in the framework of density functional theory (DFT). The value of direct band gap is found to be ~ 0.730, 0.440, 0.274, and 0.870 eV for undoped, Ag = 6.25% and 12.5% doped, and Ag= 6.25, Li= 6.25% co-doped ZnO, respectively. Acceptor levels are created at the top of the valence band and above the Fermi level in Ag and Ag-Li doped ZnO which reveals that Ag and Ag-Li are promising dopants for generating p-type ZnO. Importantly, a remarkable change in photoconductivity and optical properties are observed. The surface morphology of the spray deposited Zn_100-xAg_xO (x = 0.0–20%) and Zn_100-x-yAg_xLi_yO (x = 5, y = 0.0–10%) thin films are changed with Ag and Ag-Li contents. The XRD patterns confirmed the hexagonal structure of all the deposited films. The band gap decreases from 3.27 to 3.08 eV (for Ag doped ZnO) and increases from 3.16 to 3.38 eV for Ag-Li doping ZnO, respectively. The dielectric constants and photoconductivity spectra support the formation of p-type conductivity of Zn_100-xAg_xO and Zn_100-x-yAg_xLi_yO, which are in good agreement with the available theoretical and experimental reports. Thus, the studies performed in this work help us to understand the Ag and Ag-Li doping mechanism in ZnO; opening up possible directions toward the fabrication of p-type ZnO for advanced electronic and optoelectronic applications.