Majority Charge Carrier Transfer Studies at n-Type III-V Semiconductor-Liquid Interfaces by Impedance Spectroscopy

Stationary current/potential and impedance measurements have been conducted at different n-type III-V semiconductor-acetonitrile junctions using cobaltochenium/cobaltocene (Co(Cp)2+/0) as an outer sphere, fast redox couple. The measurements reveal that the interfacial chemistry has a strong influence on the kinetics of the charge transfer reaction. According to our impedance analysis, movement ofthe energy bands in the onset region of the forward current can be excluded for this system. For this reason a comparatively simple model can be used for the evaluation of the second order rate constants for the electrochemical charge transfer reaction across the semiconductor-electrolyte interface. The combined analysis of the stationary current/potential curves and the impedance spectra showthat the charge transfer rate ranges from about 5 x 10-12 cm4/s to 7 x 10-17 cm4/s, and is 5 - 6 orders of magnitude larger than the maximum possible rate constant predicted and reported by other researchers.