Influences of ultrasonic vibration on morphology and photoelectric properties of F-doped SnO2 thin films during laser annealing

An effective strategy, i.e. laser annealing coupled with ultrasonic vibration, was developed to improve morphology and photoelectric properties of F-doped SnO2 (FTO) thin films. The influences of vibration frequency and power were investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), UV-Vis spectrophotometer and digital four-point probe instrument. Pure laser annealing was also carried out for comparison. The results suggested that laser annealing coupled with ultrasonic vibration, rather than pure laser annealing, could significantly facilitate oriented grain growth, reduce film residual stress, enhance film compactness and uniformity, decrease film surface roughness and thickness, and thus improve photoelectric properties of the films. It was noteworthy that the appropriate vibration frequency and power were crucial to optimize the performance of the FTO films. In the present work, laser annealing coupled with ultrasonic vibration of 48 kHz and 300 W could achieve the optimal photoelectric properties of the FTO film with the highest average transmittance of 85.3% and the lowest sheet resistance of 8.8 Omega/sq, and thus yield the maximum figure of merit of 2.32 x 10(-2)Omega(-1), compared to 1.13 x 10(-2)Omega(-1) for the original FTO film and 1.29 x 10(-2) Omega(-1) for the pure laser-annealed FTO film. These results may provide a scientific basis and reference for performance optimization of transparent conducting oxide (TCO) films, and are believed to attract more interests of scientists in the research areas of TCO films and related optoelectronic applications.