Injection currents and effect of negative capacitance in porous TiO2

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Abstract
Transient dark and photocurrents and the frequency-dependent capacitance were investigated in porous (por-) TiO2 (anatase) layers. The current transients 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 potentials up to a saturation level. The drift mobility of injected electrons is 5×10−5 cm2/V s. The saturation current is described by space-charge-limited current (SCLC) in the presence of traps with an exponential energy distribution (exponential parameter, 80 meV). At high injection currents, SCLC causes slow polarization of the medium, which leads to a time-dependent capacitance and strong inductive behavior of the dark current transients.