Structural and Thermoelectric Characteristics of Sol-Gel based ZnO Thin Films Doped with Elements of Group IB

Abstract

This work presents the study results of zinc oxide (ZnO) thin films doped with elements of group IB, namely silver (Ag) and copper (Cu). The films were deposited on the Corning 1737F glass substrate using the solutions derived by sol-gel method. Effect of Ag and Cu doping on structural, surface morphology, and electrical properties were investigated. X-ray diffraction (XRD) analysis showed that both the undoped and doped ZnO thin films are polycrystalline in nature with (002) preferred orientation. The SEM images show the grown films composed with nanoparticles with sizes of about 30 to 50 nm. Doping result was verified by measurements of EDX to check compound elements, Hall effect for basic electric parameters, and UV-VIS. As a result, the EDX measurement revealed the doping ratio of Ag in ZnO as expected. Besides, the concentration of p-type carriers was between 10¹⁵ to 10¹⁷ cm⁻³, the resistivity was from 54 to 260 Ω·cm. Particularly, the band gap values were between 3.16 to 3.18 eV for the concentration of dopants between 1 to 3 mol. at% compared to that of 3.20 eV for ZnO films at room temperature. These results confirmed the success of introducing the dopants into ZnO matrix. The transport property of doped films also confirms the material nature throughout the characteristics including temperature dependence of electrical conductivity and Seebeck coefficient. In general, there was a clear change in material nature of ZnO films from n- to p-type with acceptable electrical property for thermoelectric applications.