Despite all the precautions taken, the needed precision for a defined TCS angle is beyond what can be reached with the used polishing setup. We presume that, e.g., the glue layer between sample and sample holder has a non-constant thickness. Perfect control of the TCS is however not mandatory to expose the buried interface of this junction. It is nonetheless important to be aware of it because it might induce slight deviations in the reproducibility of the TCS preparation. Total emission intensities of Ga, In, P, Ge, and O core levels were integrated (i.e., without distinction between the different states) to obtain their relative concentrations along the TCS that are depicted in Figure . The drop of the Ge elemental concentration and the rise of Ga, In, and P ones confirm an interface centered at the 8 th position. In3d emission is already evidenced at position 5, Ga at position 6, and P at position 9. This might indicate a tendency of In segregation, which was observed at a GaAs|GaInP interface, or interdiffusion into the Ge layer. It can also be noticed that the P, In, and Ga stoichiometries do not fulfill the expected Ga0.5In0.5P composition but indicate an over stoichiometry of In, 0.6:1 (Ga:P) and 1.3:1 (In:P).