Efficient photovoltaic tandem cells made of III-V semiconductors open a promising way for the realization of direct solar water splitting devices (artificial leaf) with real economic impact. The growth of an interfacial oxide separating the semiconductor from the metal catalyst brings about chemical stability and an enhancement of the charge transfer efficiency at the semiconductor-electrolyte interface. Thus, the light-induced hydrogen evolution at the illuminated front of the device can be maximized upon attainment of a particular composition and structure of the oxide. Chemical and electronic issues of the oxide grown photo-electrochemically on p-type InP(100) surfaces prepared by metalorganic vapor phase epitaxy (MOVPE) were investigated by of high-resolution surface techniques. Complementary investigations of the photo-electroplated p-type Si//In//indium-oxide interface provided a deeper insight into the influence of indium oxide and the inclusion of chloride on the photo-electrochemical activation. (C) 2017 Elsevier Ltd. All rights reserved.