Emphasis on the importance of Ga-doped ZnO thin film gas sensors fabricated by the SILAR approach for ammonia detection

Abstract This study highlights the importance of ZnO-based thin film sensors in gas-sensing applications and examines the impact of gallium concentration on their ability to detect ammonia. Ga-doped ZnO thin films were fabricated using the successive ionic layer adsorption and reaction (SILAR) method with varying doping concentrations. A series of samples was prepared, ranging from pure ZnO to films doped with 2%, 4%, 6%, and 8% Ga. The structural, morphological, and optical characteristics of the synthesized ZnO sensors were examined using various physical and chemical characterization techniques. XRD analysis confirmed that increasing the Ga doping concentration enhanced the degree of crystallization within the ZnO lattice. As the lattice parameter c increased, a corresponding decrease in the (002) diffraction intensity was observed, accompanied by a slight shift of the diffraction peaks toward lower angles. SEM observations revealed that the incorporation of Ga significantly influenced both the size and morphology of the ZnO nanostructures, likely due to its role in nucleation and crystal growth processes. Notably, a morphological transition from nanoflower-like structures to hexagonal nanodiscs was detected as the Ga doping concentration increased. Raman spectroscopy further verified the successful incorporation of Ga ions into the ZnO lattice through the observed shifts in the E 2 (high) phonon mode. The phonon mode at 439 cm⁻1, characteristic of pure ZnO, exhibited a redshift with increasing Ga content. FTIR spectra displayed distinct peaks in the low-wavenumber region (400–800 cm⁻1), corresponding to Ga–O and Zn–O vibrations, indicative of metal–oxygen bonding. With increasing Ga incorporation, minor variations in peak intensity and position were observed, confirming the substitution of Zn atoms by Ga within the lattice. Gas sensing measurements demonstrated that the fabricated films exhibited high sensitivity toward ammonia (NH 3 ) gas at room temperature. The improved response was attributed to both the morphological evolution and the electronic contribution of Ga dopants. Notably, the 6GZO sensor achieved a maximum response of 198% to 100 ppm NH 3 at 25 °C, along with fast response and recovery times of 7 and 8 s, respectively, and excellent selectivity compared to other target gases.