Investigation of physico-chemical properties of conductive Ga-doped ZnO thin films deposited on glass and silicon wafers by RF magnetron sputtering

We report on the physico-chemical properties of Undoped and Ga-doped ZnO films fabricated on glass and p-Silicon wafers at room temperature by RF magnetron sputtering using a ZnO and Ga₂O₃ mixture raw powder target without sintering procedure. X-ray diffraction (XRD) and energy dispersion spectroscopy (EDS), scanning electronic microscopy, Raman scattering, ultraviolet–visible spectroscopy, photoluminescence (PL), Hall effect and impedance spectroscopy technique have been applied for the comparative study of ZnO and ZnO:Ga thin films. XRD and Raman studies have shown that the deposited films have a preferred orientation growth with Ga atoms both in substitutional and interstitial positions. EDS analyses have allowed to show that the metallic Ga atoms have been incorporated in the ZnO films. Doping by gallium resulted in a slight increase in the optical band gap energy of the films while the optical transmittance remains about 80 %. The PL analysis at room temperature revealed violet, blue, green and red emissions. Room temperature Hall measurements show that the lowest resistivity was 3.40 × 10⁻⁴ Ω cm with an electron mobility of 18.56 cm²/V.s for an optimum Ga concentration of 4 wt%. Impedance spectroscopy study showed that σ_ac obeys the relation \(\sigma_{ac} = A\omega^{s}\). The exponent ‘‘s’’ was found to decrease with increasing the temperature. It is found that, the AC conductivity of all samples follow the correlated barrier hopping model. The Nyquist plots showed a single semicircle, indicating an equivalent circuit with a single parallel resistor R and capacitance C network. The values of the activation energy E _a deduced from both DC conductivity and relaxation frequency for all the studied samples ranged from 0.51 to 0.73 eV and the results are explained on the basis of the induced defects due to the addition of Ga into the ZnO films.