Fractional Stoichiometry of the GaAs(001)c(4×4)Surface: AnIn-SituX-Ray Scattering Study

Abstract
Synchrotron x-ray diffraction analysis of GaAs(001) epilayers grown in situ by molecular-beam epitaxy shows clear evidence of As-As dimers on top of the outermost As layer. These dimers are ordered in a variable way between two structures which both show a c(4×4) symmetry but have different As content. Both structures have twofold symmetry although the unit cell is square.