In order to compare the theoretical calculations with the surface reconstruction of Al 0.5 In 0.5 P(001) obtained experimentally, thin Al 0.52 In 0.48 P(001) layers were prepared in a horizontal MOVPE reactor using H 2 carrier gas at 100 mbar. The AlInP(001) epilayers were grown on GaInP(001) buffer layers on n-GaAs(001) substrate with 0.1 • miscut toward the [111] direction. After deoxidation of GaAs(001) substrate under tertiarybutylarsine at 620 • C (surface temperature), 100 nm GaAs(001) and 100 nm GaInP(001) buffer layers were grown. Tertiarybutylphosphine (TBP), trimethylindium (TMIn), trimethylgallium (TMGa), and trimethylaluminium (TMAl) were used as precursors. The epitaxially grown layers were doped n-type (∼ 1×10 17 cm -3 ) using ditertiarybutyl silane (DTBSi). The Al 0.52 In 0.48 P(001) layer was grown at 100 mbar with a V/III ratio of 60 at 600 • C. To compensate the desorption of P from the AlInP(001) surface during cooling, the TBP precursor was kept open until reaching 300 • C. Subsequently, the TBP precursor was switched off and the sample was annealed for 10 min at 310 • C to remove the excess of P and TBP precursor residuals from the surface. Lattice matching of the GaInP(100) and Al-InP(001) layers to the substrate was confirmed ex situ by X-ray diffraction (XRD) in reference samples. In order to investigate the surface reconstruction and chemical com- FIG. XPS survey spectrum of a 32 nm-thick Al0.52In0.48P(001) layer (top) as well as the Al 2p, In 3d 5/2 , and P 2p core-level photoemission lines measured at 30 • (middle) and 90 • (bottom) take-off angle (with respect to surface plane).