Extended x-ray-absorption fine-structure study of hydrogenated amorphous silicon-germanium alloys. I. Analysis based on spherical waves of photoelectrons

In conventional EXAFS (extended x-ray-absorption fine-structure) analyses, reliable structures are obtained with different values of absorption-edge energy $E_0$ for different neighboring atoms. It is shown in this study that the Ge K-edge EXAFS resulting from the Ge-Ge and Ge-Si bonds in hydrogenated amorphous Si-Ge alloys can be excellently explained by a unique $E_0$ value provided that a newly developed formula based on the spherical wave functions of photoelectrons is employed. The $E_0$ value is just at the steepest point in the experimental edge-jump curve. With the conventional formula the adjusted $E_0$ values for the Ge-Ge and Ge-Si bonds differ by 7 eV at maximum, and in addition they deviate by 3 eV at least from the steepest point.