Toshimi Nagase

A Novel Method for the Preparation of Green Photoluminescent Undoped Zinc Oxide Film Involving Excimer Laser Irradiation of a Sol-Gel-Derived Precursor

A green photoluminescent (PL) undoped zinc oxide film was successfully prepared by a novel method involving KrF excimer laser irradiation of a sol-gel-derived precursor. This method requires the appropriate energy fluence (Ef) of 100 mJ/cm2 of the laser, and has the advantage of practical production at a low substrate temperature of 473 K in air. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) observations showed that the green PL film has close-packed columnar crystals in an upper layer, where the green PL centers involving oxygen vacancies are presumed to be present.

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 nm 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≥100 mJ/cm2 produced crystal growth of close-packed ZnO crystals in an upper layer. Laser irradiation at a high Ef (150 mJ/cm2) 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≥100 mJ/cm2 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/cm2); 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.

Green Cathodoluminescence Properties of Zinc Oxide Films Prepared by Excimer Laser Irradiation of a Sol-Gel-Derived Precursor.

Green cathodoluminescent (CL) zinc oxide (ZnO) films were successfully prepared at a low substrate temperature (473 K) in air by KrF-excimer laser irradiation of a sol–gel-derived precursor (ELISG method). Structures and CL properties of the films irradiated by the laser at different energy fluences (Ef) were studied and compared with those of a film prepared by conventional heat treatment in a reducing atmosphere. The prepared ZnO films showed a green CL band peaking at around 510 nm, in addition to an ultraviolet CL band. The maximum intensity of the green CL was obtained from a film produced by laser irradiation at an Ef of 130 mJ/cm2. Near-IR spectroscopy suggested that the green CL intensity depends on free-carrier concentration of the films and is maximized at an appropriate concentration. The formation process of the green CL films by the ELISG method was discussed in terms of thermal and photoinduced effects induced by the laser irradiation.

Crystalization of sol-gel derived precursor zinc oxide file during KrF excimer laser irradiation

The present paper describes a study on the crystallization of a sol-gel derived precursor ZnO film during and after the irradiation of an excimer laser. The temporal change of the structure of ZnO films was discussed based on the time-resolved signal of a reflected and a transmitted laser beam during the excimer laser irradiation. The surface morphology of the films was analyzed by atomic force microscope (AFM). The pulse-to-pulse changes of integrated signals reflected the surface conditions of the ZnO film. In time-resolved measurement, significant changes of both signals were observed during the first pulse.