Morphology, structure and photoluminescence properties of zinc oxide films prepared by excimer laser irradiation of sol-gel-derived precursors

Morphology, structure and photoluminescence (PL) properties of zinc oxide (ZnO) films prepared by KrF-excimer-laser irradiation of sol-gel-derived precursors were studied. The precursors with a film thickness of 100 or 180 nun were irradiated by the laser at various energy fluences (Ef). Atomic force microscopy and transmission electron microscopy observations revealed that the laser irradiation at an Ef greater than or equal to 100 mJ/cm(2) produced crystal growth of close-packed ZnO crystals in an upper layer. Laser irradiation at a high Ef (150 mJ/cm(2)) of the thinner precursor produced a remarkable crystallization throughout the film, resulting in larger grain size and smooth film surface. Our observation results suggest that the crystallization proceeds by sintering or solidification via melting. The films obtained at Ef greater than or equal to 100 mJ/cm(2) showed green PL. The PL spectra were not significantly influenced by the excitation wavelength except for the thinner film irradiated at a high Ef (150 mJ/cm(2)), it showed a striking increase in the green PL intensity when excited at 275 nm instead of 325 nm. The unique excitation-wavelength dependence may be related to its characteristic threshold of electron excitation.