Ultrafast electrochemical charge-transfer reactions at III-V semiconductor-molecule interfaces

The kinetics of the majority charge-transfer between GaAs and the cobaltoce ne-co-baltocenium (Co(Cp)(2)(+/0)) redox system in acetonitrile has been st udied in the dark using electrochemical impedance spectroscopic (EIS) and c urrent-voltage techniques. Additionally conducted quartz crystal microbalan ce measurements reveal that the Co(Cp)(2)(+/0) molecules physisorb at the G aAs surface. The physisorption of the redox molecules is in a,agreement wit h the electrochemical investigations and has to be considered for the devel opment of a model describing the overall charge-transfer. The charge-transf er model will be briefly discussed. A detailed analysis of the EIS based on the model leads to the conclusion that the electron transfer from the GaAs conduction band to the adsorbed Co(Cp)(2)(+/0) molecules and the subsequen t electron transfer to the redox species in solution are so fast, that the transport of electrons through the space charge region of the semiconductor becomes the current limiting mechanism.