X-ray-absorption near-edge structure of ${\mathrm{CuGaSe}}_2$ and ZnSe: Experiment and theory

X-ray-absorption near-edge structure (XANES) spectra of a ternary semiconductor ${\mathrm{CuGaSe}}_2$ at the Cu, Ga, and Se edges were measured and compared with Zn and Se spectra of ZnSe, taken from the literature. Having all five absorbing atoms in nearly identical coordination environments, we investigate the influence of the electronic structure on the XANES spectra. The spectra of ${\mathrm{CuGaSe}}_2$ and of ZnSe were calculated using a real-space multiple-scattering approach and using a pseudopotential band-structure technique. Both computational methods yield spectra that are in a good agreement with experiment. The effect of the size of the cluster involved in the real-space calculation on the calculated XANES spectra is investigated. Using self-consistent muffin-tin potentials does not lead to significantly different ${\mathrm{CuGaSe}}_2$ spectra than using non-self-consistent potentials. Real-space multiple-scattering spectra calculated without core holes exhibit only minor differences with respect to those obtained for relaxed screened core holes, the largest effect being found for Zn spectrum of ZnSe. Employing unrelaxed or unscreened core hole potentials resulted in spectra that did not agree with experiment. Contrary to earlier reports, no effect of charge transfer on the calculated XANES spectra of ZnSe was found.