Structure at the Yb/GaAs interface studied by anomalous x-ray scattering

Different 4×1 superstructures are found for Yb/GaAs(001) contacts with different Yb thicknesses. To clarify the role of Yb atoms in the 4×1 structure, an x-ray anomalous-dispersion effect has been used in the grazing-incidence x-ray-diffraction geometry. Diffraction intensities measured in the x-ray energy range near the Yb ${\mathit{L}}_{\mathrm{III}}$ absorption edge show a characteristic variation, which reflects the energy dependence of the real part of the anomalous scattering factor (f’) for Yb atoms. As a result, for all the samples, Yb atoms are found to order in 4×1 structures. The arrangements of the Yb atoms in the 4×1 unit cell are derived from Buerger’s decomposition method of the Patterson function. By comparison of the calculated diffraction intensities with observed intensities, two different (4×1) structural models for the thin and thick Yb-layer samples are found. Different Schottky-barrier-height values are also found for these samples.