Photoelectrochemical behavior of n-GaAs and n-AlxGa1-xAs in CH3CN

Current density vs potential, open-circuit voltage vs temperature, and diff erential capacitance vs potential measurements have been used to show that n-GaAs and n-AlxGa1-xAs electrodes exhibit partial Fermi level pinning in c ontact with CH3CN over a wide range of redox potentials. Despite a change o f over 1.2 V in redox potential of the solution, the open-circuit voltage o nly changed by similar to 300 mV. The slope of the opencircuit voltage vs r edox potential of the solution was typically 0.33-0.44. Differential capaci tance vs potential data also yielded a barrier height change of less than 3 00 mV for over 1.2 V change in the redox potential of the solution. The dep endence of the current density vs potential behavior of n-GaAs/CH3CN-ferric enium-ferrocene(+/0) on variables such as the illumination intensity, dopan t density of the semiconductor, concentration of redox acceptor in the solu tion, crystal face, electrolyte, and cell temperature was evaluated. The re sultant kinetic data indicate that surface-state recombination is the domin ant recombination mechanism at these interfaces, which are capable of produ cing an open-circuit voltage of 0.83 V at a short-circuit current density o f 20 mA cm(-2), as well as energy conversion efficiencies of > 10%. X-ray p hotoelectron spectroscopy investigation of n-GaAs confirmed surface changes were induced by electrochemical operation of n-GaAs electrodes in CH3CN-co baltocenium-cobaltocene(+/0) electrolyte. The presence of Fermi level pinni ng and the existence of changes in n-GaAs and n-AlxGa1-xAs electrode surfac es when these electrodes are in contact with CH3CN-cobaltocenium-cobaltocen e(+/0) electrolyte complicates the extraction of k(et) values from the stea dy-state current density vs potential behavior of n-GaAs or n-AlxGa1-xAs/CH 3CN contacts.