Work function tuning and fluorescence enhancement of hydrogen annealed Ag-doped Al-rich zinc oxide nanostructures using a sol-gel process

Abstract

Effect of incorporation of Ag on the structural, optical, electrical, and fluorescence properties of sol-gel derived Al-rich zinc oxide (ZnO:Al:Ag) nanostructured films was studied. The E<inf>g</inf> of the film slightly decreased to a minimal value with Ag doping, and was found to be about 3.65 eV for R<inf>Ag/Zn</inf> = 1% from its initial value of 3.72 eV (R<inf>Ag/Zn</inf> = 0%). The WF sudden increased to a maximal value of 5.12 eV with Ag doping (for R<inf>Ag/Zn</inf> = 1%) from its initial value of 4.73 eV for R<inf>Ag/Zn</inf> = 0% due to substitution of Ag into Zn sites until saturation was achieved (R<inf>Ag/Zn</inf> = 1%). After more Ag doping, WF started to decrease and finally, reached a value of 4.81 eV for R<inf>Ag/Zn</inf> = 3% because of the formation of an impurity-defect energy level below the intrinsic Fermi level of ZnO. With Ag-doping, the current increased up to R<inf>Ag/Zn</inf> = 1% due to the increase in carrier density. For R<inf>Ag/Zn</inf> = 3% doping, the current density started to increase due to the influence of metallic Ag. The defective peak position was blue shifted, with increased Ag-doping, from 536 nm (R<inf>Ag/Zn</inf> = 1%) to 527 nm for R<inf>Ag/Zn</inf> = 2% due to the sizes of the Ag+ and Zn2+ ions. The FL defective peak intensity (I<inf>D</inf>) in the green region increased with the concentration of Ag used for doping, up to R<inf>Ag/Zn</inf> = 2%. The enhancement in the I<inf>D</inf> may be due to charge difference between the Zn2+ ions, caused by Ag+ ions. © 2015 Elsevier B.V. All rights reserved.