XPS STUDIES OF OXIDE LAYERS ON INP AFTER OXIDATION IN THE PRESENCE OF CE-4+

Quantitative XPS analyses are carried out to study the III-V semiconductor/solution interface. In the presence of ceric ions (Ce4+) solvated in sulphuric acid (H2SO4, 0.5-2 M), III-V compounds undergo a dissolution which is completely governed by an electrochemical process. Competition between a superficial oxide growth and its quasi-simultaneous dissolution determines the behaviour of the interface as a function of time. On InP some typical surface evolutions are observed, such as a decrease in the hole injection current during the reduction of cerium oxidized species. In order to explain this blocking effect, we have analysed the chemical composition of InP surfaces by XPS after oxidation in the presence of cerium ions. We report here the evolution of the oxide layer formed at the semiconductor/electrolyte interface in relation to the dipping time of the electrode and the cerium and sulphuric acid concentrations. It is observed that the lower the pH, the more soluble is the oxide layer. Moreover, increases in the cerium concentration and dipping time enhance the growth of a complex oxide layer. This layer is rich in oxidized phosphorus and strongly depleted in indium. Profiling of the layer shows a cerium distribution all over the oxide layer. The electrochemical behaviour of InP samples changes in relation to the properties of this complex multiphase film.