Nanosecond-laser annealing of zinc oxide thin-films: the effect of the laser wavelength and fluence

Zinc oxide thin-films were grown via RF-magnetron sputtering, and irradiated with a nanosecond laser at distinct wavelengths (266, 355, 532, and 1064-nm) and fluences (20-3000mJ/cm²). The structural, chemical, and topological properties of the laser-irradiated films were then characterized using X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and scanning electron microscopy (SEM), and compared to samples annealed by a conventional thermal process. It was found that samples irradiated with UV light at a fluence higher than ∼100 mJ/cm² exhibit high crystallinity. XRD revealed that the crystallized ZnO films consist of a single-phase, with grain-size as large as 35nm. The stoichiometry of the irradiated film determined from the RBS analysis becomes close to 1:1 oxygen-to-zinc ratio as the laser fluences increases. SEM images show a smooth and ordered surface with spherical nanostructures. Laser annealing technique discussed in this work may find wide applications in the semiconductor industry due to a relatively short annealing time compared to thermal annealing.