Direct Measurement of Valence Charge Asymmetry in GaAs Using X-Ray Standing Waves
E Nelson, Joseph Woicik
Through detection of valence photoelectrons, the technique of x-ray standing waves directly measured the charge asymmetry of the GaAs valence band. Using the back-reflection geometry for the (111) and (111) diffraction planes, we determine from the coherent distances of the standing waves, that a majority of the valence electrons reside on the As atoms of this heteropolar crystal. These measurements agree well with the GaAs bond polarity calculated from the values of the Hartree-Fock terms. In contrast, the valence standing waves for germanium determine the valence charge to be symmetric. The coherent fractions of the standing waves of Ge and GaAs are reduced compared to those of core-level standing waves, indicating the delocalization of valence charge. This technique using low energy x-rays together with valence photoelectron detection can be more generally applied to the study of chemical bonding.
Journal of Synchrotron Radiation
body polarity, valence band photoemission spectroscopy, x-ray standing waves