Measurement of Interfacial Charge-Transfer Rate Constants at n-Type InP/CH 3 OH Junctions

Steady-state current density vs potential methods have been used to measure interfacial electron-transfer rate constants at n-type indium phosphide/liquid junctions. n-InP/CH 3 OH-1,1‘-dimethylferrocene +/0, n-InP/CH 3 OH-ferrocene +/0, n-InP/CH 3 OH-tetrahydrofuran-decamethylferrocene +/0, and n-InP/CH 3 OH-1,1‘-diphenyl-4,4‘-dipyridinium 2+/+• contacts displayed bimolecular kinetic behavior in which the observed current density was first order in the concentration of electrons at the semiconductor surface and in the concentration of acceptors in the solution. Differential capacitance potential measurements were used to determine the energetics for the charge-transfer process as well as to determine the concentration of electrons at the semiconductor surface as a function of applied potential. These measurements indicated that the voltage dropped across the semiconductor space charge region varied linearly with changes in the Nernst potential of the solution, as expected for an ideally behaving semiconductor/liquid junction. The measured charge-transfer rate constants, k et, for these systems were ≈10 -16 cm 4 s -1, in excellent agreement with previous theoretical predictions.