Ultraviolet-reduced reduction and crystallization of indium oxide films

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 O^2- 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.