FLAT-BAND 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/H2SO4 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 (phi(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 phi(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.