Anisotropy of persistent photoconductivity in oxygen-deficient YBa2Cu3Ox thin films

YBa2Cu3Ox (x approximate to 6.6) thin films were deposited by pulsed-laser ablation on SrTiO3 substrates, that were cut with a tilt angle alpha=10 deg rees with respect to the [001] direction, inducing a steplike growth of the CuO2 layers. The films appeared semiconducting along the projection of the c axis to the film surface, but metallic in the perpendicular direction. F rom the anisotropic resistance, the in-plane (rho(ab)) and the out-of-plane (rho(c)) resistivities were calculated. Photodoping with white light was p erformed at various temperatures from 70-305 K. We have found strongly temp erature dependent photoinduced decreases of rho(ab) and rho(c). At low temp eratures, the relative reduction of rho(c) was smaller than that of rho(ab) , whereas, near room temperature, they were nearly the same. The electrical anisotropy rho(c)/rho(ab) increased monotonously at 70 K, but, at higher t emperatures, a fast increase was followed by a long-term decay. This unusua l behavior resembles that of the in-plane Hall mobility in a previous study , suggesting that both quantities are changed by the same physical process. The results are discussed within the models previously proposed for the ph otodoping effect in YBa2Cu3Ox. [S0163-1829(99)11833-2].