Flatband Potentials, Barrier Heights, and Charge Transfer at the n ‐ InP / Electrolyte Contact

Current voltage curves, Mott‐Schottky data, and impedance spectroscopic measurements are taken at the n ‐ InP / H 2 SO 4 contact for bare and Pt‐coated electrodes. In the transition range from anodic to cathodic currents ( H 2 evolution) drastic changes of the electrode response occur ( i.e. , changes in reverse current densities, barrier heights ( φ B ) , photovoltages, and impedance response) whereas flatband potentials derived from Mott‐Schottky measurements remain essentially constant. These results recall to mind the barrier height as a fundamental parameter defining the interdependence of flatband and redox potential. Barrier heights are discussed in terms of the Schottky diode theory with a decrease in φ B attributed to hydrogen saturation of the metal ( n ‐ InP ‐ Pt ) or to cathodic corosion of bare n ‐ InP (formation of a quasi‐ohmic contact n ‐ InP ‐ In ). Parameters of the electrochemical charge‐transfer reaction and parameter changes of the semiconductor/surface barrier at n ‐ InP ‐ Pt are separated with impedance spectroscopy. Results are used for the discussion of Tafel slopes of semiconductor electrodes in the forward bias range.