Effects of high dose gamma irradiation on ITO thin film properties

Abstract

Transparent thin-film Indium Tin Oxides (ITO) were prepared on 0.7mm thick glass substrates using a pulsed laser deposition (PLD) process with average thickness of 150nm. The samples were then exposed to high gamma γ radiation doses by 60Co radioisotope. The films have been irradiated by performing exposure cycles up to 250kGy total doses at room temperature. The surface structures before and after irradiation were analysed by x-ray diffraction. Atomic Force Microscopy (AFM) was performed on all samples before and after irradiation to investigate any change in the grain sizes, and also in the roughness of the ITO surface.We investigated the influence of γ irradiation on the spectra of transmittance T, in the ultraviolet-visible-near infrared spectrum using spectrophotometer measurements. Energy band gap Eg was then calculated from the optical spectra for all ITO films. It was found that the optical band gap values decreased as the radiation dose was increased.To compare the effect of the irradiation on refractive index n and extinction coefficient k properties, additional measurements were done on the ITO samples before and after gamma irradiation using an ellipsometer. The optical constants n and k increased by increasing the irradiation doses. Electrical properties such as resistivity and sheet resistance were measured using the four-point probe method. The good optical, electrical and morphological properties maintained by the ITO films even after being exposed to high gamma irradiation doses, made them very favourable to be used as anodes for solar cells and as protective coatings in space windows.