Potential dependent transient microwave photoconductivity at the ZnO/electrolyte interface

Transient microwave photoconductivity measurements with pulsed laser excitation have been performed on a monocrystaline ZnO electrode in contact with aqueous electrolyte. The decay time (tau) is related to decay in the concentration of photoinduced charge carriers at the semiconductor-electrolyte interface. Measurements are carried out at different values of applied potential in the electrochemical cell, i.e. band bending in the semiconductor space charge layer (SCL), and different intensities of the laser pulse. At a lower pulse intensity, t shows a pronounced maximum under low depletion conditions in the SCL. Such behaviour is not observed at higher intensity where t only slightly decreases with the applied voltage. The maximum in the decay time is related to a maximum in the stationary microwave conductivity signal reported in previous papers, and reflects longer lifetime of minority carriers under low depletion conditions. Microwave absorption transient techniques can be used for fast kinetic studies in photoetectrochemistry, by passing the typical time response constraints of other techniques.