Potential dependent transient microwave photoconductivity at the ZnO/electrolyte interface

Transient microwave photoconductivity measurements with pulsed laser excita tion have been performed on a monocrystaline ZnO electrode in contact with aqueous electrolyte. The decay time (tau) is related to decay in the concen tration of photoinduced charge carriers at the semiconductor-electrolyte in terface. Measurements are carried out at different values of applied potent ial in the electrochemical cell, i.e. band bending in the semiconductor spa ce charge layer (SCL), and different intensities of the laser pulse. At a l ower pulse intensity, t shows a pronounced maximum under low depletion cond itions in the SCL. Such behaviour is not observed at higher intensity where t only slightly decreases with the applied voltage. The maximum in the dec ay time is related to a maximum in the stationary microwave conductivity si gnal reported in previous papers, and reflects longer lifetime of minority carriers under low depletion conditions. Microwave absorption transient tec hniques can be used for fast kinetic studies in photoetectrochemistry, by p assing the typical time response constraints of other techniques.