ANALYSIS OF PERSISTENT PHOTOCONDUCTIVITY ON OXYGEN-DEFICIENT YBA2CU3O7-X THIN-FILMS

Fully oxygenated epitaxial thin films of YBa2Cu3O7-x with thicknesses between 100 and 300 nm were deposited by a de high oxygen pressure spu ttering method on (001) SrTiO3 substrates. From these films we have ob tained samples with different oxygen deficiency x between 0.2 to 0.8, using a thermal treatment. These films were illuminated at 10K, 95K, 2 73K and near room temperature with 632.8 nm laser light for more than three hours. The change of the conductivity during and after illuminat ion was fitted according to the Kohlrausch expression Delta sigma(t) = Delta sigma(O)exp[-(t/tau)(beta)]. The relaxation time tau and the di spersion parameter beta depend strongly upon oxygen content and temper ature during illumination. This behavior indicate that persistent phot oconductivity (PPC) in these films may be due to trapping of electrons in the Cu-O chains. This suggests the existence of a large energy bar rier impeding the electrons to recombine and finally holes are transfe rred to the CuO2 planes enhancing the conductivity.