In situ Modification of the Energetic Structure of the n-GaP/NH3 Junction in the Presence of Solvated Electrons.

Band-edge shifts of the n-GaP/electrolyte junction, when the pH and solution redox potential vary, are demonstrated in situ. Large variations (14 pH units and more than 2 V) of these parameters are obtained by using liquid ammonia solutions (neutral and basic) in the presence and absence of solvated electron species. The semiconductor band-edge position was deduced from Mott-Schottky curves in the following ammonia solutions: neutral, solvated electron, basic, basic + solvated electron, basic and basic + solvated electron. The transformation of a solution to the next one was obtained in situ, i.e. without removing the electrode from the solution. Large band-edge shifts could be demonstrated, up to ΔVfb = −1.8 V between the first solution (neutral) and the last one (basic + solvated electron). A reversible band-edge shift was observed between the basic and basic solvated electron solutions. The photoelectrochemical study revealed classical semiconductor/electrolyte behaviour with large photovoltages (up to 1.75 V in the solvated electron solution). The GaP/solvated electron junction behaviour gives some information to the more general investigation concerning the contact of a semiconductor and a redox system, the potential of which is located within the material conduction band.