Enhanced charge transport properties of Ag and Al co-doped ZnO nanostructures via solution process

Conducting Ag and Al co-doped ZnO (ZnO:Al:Ag) nanostructures were synthesized using sol-gel process. The effects of Ag incorporation on the structural, optical, electrical, and photoluminescent properties of ZnO:Al:Ag nanostructures were studied. The crystalline quality of the nanostructures was found to be improved by Ag doping concentration of 0.3% owing to compensation for vacancies created by Al³⁺ via Ag⁺. The electrical properties were enhanced for Ag doping concentration of 0.3%. This may be due to an improvement of the crystalline quality. The optical band-gaps (E_g) of the nanostructures are significantly lower than that of undoped ZnO. The E_g of the nanostructures slightly decreased to its minimal value with Ag doping, and was found to be about 3.19 eV for R_Ag/Zn = 0.3%; the material then retained its initial value of 3.22 eV (R_Ag/Zn = 0%) for higher Ag doping. With Ag doping, the value of work function (WF) increased from 4.67 eV for R_Ag/Zn = 0% to 4.99 eV for R_Ag/Zn = 0.3% due to substitution of Ag⁺ into Zn²⁺ sites. An absorption peak in the blue region was observed in the Ag-doped nanostructures; this peak redshifted with the increase of the doping concentration. The photoluminescence (PL) intensity in the near band edge (NBE) region was the highest for the Ag/Zn ratio of 0.3%, whereas the maximum PL intensity in defect region was obtained for the Ag/Zn ratio of 0%.