Injection currents and effect of negative capacitance in porous TiO2

Transient dark and photocurrents and the frequency-dependent capacitance we re investigated in porous (por-) TiO2 (anatase) layers. The current transie nts consist of a fast part being characteristic for a transit of charge and of a slow part which increases strongly in time for high applied potential s up to a saturation level. The drift mobility of injected electrons is 5x1 0(-5) cm(2)/V s. The saturation current is described by space-charge-limite d current (SCLC) in the presence of traps with an exponential energy distri bution (exponential parameter, 80 meV). At high injection currents, SCLC ca uses slow polarization of the medium, which leads to a time-dependent capac itance and strong inductive behavior of the dark current transients. (C) 20 01 American Institute of Physics.