Mechanism of Ag Doping in ZnO Nanowires by Electrodeposition: Experimental and Theoretical Insights

A range of complementary techniques was used to explore the physical mechanisms of Ag doping in ZnO nanowires obtained by a low-temperature electrochemical process. Cyclic voltammetry analysis was employed to demonstrate the ability of Ag to modify the electrochemistry and in turn the ZnO growth environment generating amenable conditions for p-type doping. Both X-ray photoelectron spectroscopy and calculations using density functional theory (DFT) showcase that the principal Ag impurity in the nanowires is Ag substitution for Zn (Ag-Zn). The calculations also indicate that Ag-Zn doping forms an impurity band because of Ag 4d and O 2p orbital interactions shifting the Fermi level toward the valence band. Electrical characterization of the Ag-doped nanowires confirms the observations in the DFT calculations. It was also found that the formation of Ag acceptors is favorable under O rich growth conditions which can be experimentally tuned. The combination of experimental and theoretical studies performed in this work helps us to understand the Ag-doping mechanism in low-temperature growth opening up possible directions toward highly conductive p-type ZnO for advanced optoelectronic applications.