Structural and morphological characterization of sol-gel ZnO:Ga films: Effect of annealing temperatures

Sol-gel technology has been successfully applied for obtaining ZnO:Ga films by spin coating method. Their structural and optical properties are studied depending on the doping contents and on the annealing temperatures varying from 300 to 600 °C. The Ga doping has been achieved by dissolving 1, 2 and 3 wt% Ga(NO3) into Zn sol solution. The structural analysis performed by X-Ray diffraction (XRD) shows a deterioration of the film crystallization with gallium incorporation. The XRD study reveals no impurity peaks associated to metallic gallium or gallium oxide phases. Vibrational properties have been characterized by Fourier Transform Infrared (FTIR) spectroscopy. FTIR analysis gives no certain evidence for presence of Ga oxide phases, but the absorption bands are clearly affected by Ga additive and there can be possible overlapping of ZnO and GaO vibrations. The sol-gel ZnO:Ga films possess higher transparency in the visible spectral range compared to zinc oxide films. The optical band gaps of ZnO:Ga films are found to be widening due to gallium doping. The film morphology is investigated by Atomic force microscopy and it has been found that Ga doping in ZnO affects significantly the film morphology. The surface roughness of ZnO:Ga films is smaller compared to ZnO.