Dynamics of photodoping and photoconductivity relaxation in oxygen-deficient YBa2Cu3Ox

Studies of the time evolution of the photodoping process and of the relaxation of persistent photoconductivity (PPC) in oxygen-deficient YBa2Cu3Ox are presented. We show that the resistance decrease during white light illumination of the samples does not saturate up to photon doses of 10(23)-10(24) cm(-2). The efficiency of the photodoping process is weakly temperature dependent, decreasing at low temperatures for extended illumination. The relaxation of PPC follows a Kohlrausch law with the time constant of several hours near room temperature and more than 1200 h at 254 K. Similarly to semiconducting samples, the temperature dependence of the relaxation rate follows the thermal activation process across an energy barrier of approximate to 0.9 eV. However, the dispersion parameter exhibits in our case the opposite temperature dependence it increases with the temperature decrease. There is no indication of a threshold temperature around 270 K. The observed behavior suggests that two different mechanisms contribute to the photodoping process.