Influence of Ga dopant on photoelectrochemical characteristic of Ga-doped ZnO thin films deposited by sol–gel spin-coating technique

In this study, Ga-doped ZnO thin films were prepared using sol–gel technique via spin-coating method. The effect of Ga-doping dopant (0, 1, 2 and 3 at.%) on microstructural, optical, electrical and photoelectrochemical (PEC) characteristics have been investigated. The spin-coating was repeated six times, and as-obtained thin films were then annealed at 500 °C for 1 h in vacuum. After annealing, all samples revealed single phase of hexagonal ZnO polycrystalline structure with a main peak of (002) in X-ray diffraction (XRD) pattern. Raman spectra show that the vibration strength of E₂ is highly decreased by Ga doping. Thicknesses of all samples were ~300 nm measured via scanning electron microscopy (SEM) cross-section images and alpha-step. The optical band gap and resistivity of samples were in the range of 3.24 to 3.28 eV and 102 to 9 Ohm cm, respectively. Resulting from PEC response, the 2 at.% Ga-doped ZnO thin film has a better PEC performance with photocurrent density of ~0.14 mA/cm² at 0.5 V versus saturated calomel electrode (SCE) under illumination with the intensity of 100 mW/cm². This value was about seven times higher than the un-doped film (reference sample). Observed higher photocurrent density was likely because of a suitable Ga-doping concentration causing a lower resistivity.