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Structural changes stimulated by ultraviolet (UV) irradiations of sol–gel-derived indium oxide thin films were investigated. Illumination of incoherent UV photons (4.9 eV) from a low-pressure mercury lamp resulted in formation of crystalline indium metal. Irradiation of coherent UV beams from an ArF excimer laser (6.4 eV) and from the fourth harmonics of a Nd:YAG laser (4.7 eV) was found to be effective in the crystallization of indium oxide, accompanied by a decrease in the sheet resistance. The lowest resistance without a reduction of transmission in the visible region was achieved with a 6.4 eV laser beam at a fluence over 10–20 mJ cm−2 shot−1. The results of x-ray photoelectron spectroscopy revealed that charge transfer from O2− to In3+ was induced by the incoherent and the coherent UV photons. The partial reduction with the incoherent illumination and the crystallization with the laser irradiation are tentatively assumed to be due to electronic excitations in the amorphous network.

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Structural changes stimulated by UV light irradiation for sol-gel-derived amorphous ZnO were investigated. Transformation of amorphous ZnO into the wurtzite phase was achieved by irradiation of 4.9 eV photons in air using a conventional low-pressure mercury lamp. On the other hand, the crystallization was not observed by UV irradiation in vacuum. Cleavage of the Zn–O network with electronic excitation and subsequent oxidation with activated oxygen species are deduced to be essential for the formation of the ordered structure from the amorphous phase.