High energy photon induced Fermi-level shift of Ba0.5Sr0.5TiO3 thin films

We have studied surface chemical states of Ba0.5Sr0.5TiO3 (BST) thin films as a function of high energy photon doses. BST thin films were deposited on Si substrates by Sputtering technique and post irradiations were carried out with high energy 60Co gamma radiation. Core-level and Fermi-level spectra were measured by X-ray photoelectron spectroscopy. The gamma-ray irradiated BST films showed a higher binding energy shift of Ba, Sr, and Ti core level with increasing gamma doses due to shift in Fermi level. The Fermi level is shifted towards conduction band by ~ 1.1 eV for 200 kGy gamma irradiated BST with respect to pristine. An increase in full width at half maximum of X-ray diffraction peak and surface roughness were also observed with increasing gamma doses. Higher leakage current and decrease in capacitance with gamma doses are further evidence of higher carrier concentration which is consistent with the shift in Fermi level.