Effects of dopant (Al, Ga, and In) on the characteristics of ZnO thin films prepared by RF magnetron sputtering system

The un-doped and Al, Ga, and In doped (3 wt.%) ZnO thin films have been prepared on glass substrates using RF magnetron sputtering at 350 °C. The effects of these dopants on the structural, morphological, electrical, and optical properties of deposited films have been studied. XRD study showed that all doped ZnO thin films have the polycrystalline nature with hexagonal wurtzite phase having c-axis preferred out-of-plane orientation. The cross-sectional FE-SEM micrographs showed that all the films have columnar structure. AFM images showed that doped ZnO thin films have better surface smoothness than un-doped ZnO thin films regardless of doping elements. The GZO thin film have the optimal electrical properties among all doped samples in terms of the carrier concentration (6.13 × 10²³ cm^-3), charge carrier mobility (28.2 cm² V^-1 s^-1), and a minimum resistivity (3.61 × 10^-4 Ω cm). UV-Vis spectrometer results showed that all the films are highly transparent in the visible region and the band gap energy of the films varies from 3.25 eV to 3.75 eV for the different dopants. PL spectra showed the un-doped and doped ZnO thin film exhibited a violet emission in the 390-405 nm range, with different intensities, which is due to difference in concentration of zinc vacancies.