The interface formation between Cobalt and In0.48Ga0.52P(004) has been studied using soft x-ray photoemission spectroscopy (SAPS), low energy electron diffraction (LIED), and scanning tunneling microscopy. For room temperature deposition the first monolayer of Co decorates C p homogeneously the InGaP(001)(2x4) dimer rows. The surface morphology, e.g., step distribution, is conserved leading to a smooth (0.8 nm roughness) surface, however no evidence for crystalline bee Co was observed with LEED. SXPS spectra reveal that the In 4d and Ga 3d core level contain metallic components shifted to lower binding energies, that are related to InCo/GaCo compounds forming at the interface. In contrast to Co reactions with GaAs where As is diffusing to the top we found that the intensity of the P2p core level decreases after deposition of 20 ML Co. The In and Ga intensity instead remain prominent, thus even after the deposition of 20 ML of Co the reactions have not stopped. Growth experiments at higher substrate temperature (150 degreesC) showed that the enhanced mobility of the species favors island growth and therefore leads to a higher surface roughness of 2-3 nm, whereas the film does not show epitaxial quality as confirmed with LEED. (C) 2003 American Vacuum Society.