EXAFS and XANES study of GaAs on Ga and As K edges

The extended X-ray absorption fine structure (EXAFS) at the K edges of Ga and As has been calculated in the multiple-scattering approach using the fast spherical approximation. It is shown that, for both edges, multiple-scattering contributions are negligible for wavevector values greater than 3 AA ^-1, and the single-scattering analysis can be used without significant loss of accuracy in that region. The calculated spectra are in good agreement with measurements at 77 K. The X-ray absorption near-edge structure (XANES) at both edges have been calculated by the continued-fraction expansion method. The origin of the main XANES features and the differences between Ga and As edges have been interpreted. The first main peak is attributed to the bound-to-bound 1s to 4p transition. The second feature is a scattering resonance within the second coordination shell: its position is defined by the different phase shifts of the photoelectron wave under scattering from the Ga or As atoms.