From the 1 st to the 13 th position, As has been detected while In and P are detected between the 9 th and the 20 th position. This can also be seen in Figure where the relative concentration profile of this interface is plotted. We, therefore, describe the TCS structure as followed: the 1 st to the 8 th positions correspond to the n-GaAs(100) wafer while the 14 th to the 20 th positions correspond to pure GaInP. Between these positions, there is the interface centered at position 10 (see white dotted line in Figure ). The core level spectra of As3p and P2p (Figure ) show the GaAs state, for which the intensity is declining, as well as the GaInP state, for which the intensity is rising. This can also be observed with the relative concentration profile depicted in Figure .