ANALYSIS OF RHEED DATA FROM THE GAAS(001)2X4 SURFACE

Dynamical calculations of sets of clastic RHEED rocking curves from the (2 x 4)-reconstructed GaAs(001) surface, using 12.5 keV electrons incident in the (110BAR) azimuth, are presented. Comparison of theoretical curves with experimental data permits an estimate of the values of the parameters present in the assumed surface model. The reliability of the parameters obtained is discussed with reference to factors possibly limiting the closeness of fit attainable between theory and experiment, notably inconsistencies in the experimental data and the neglect of the possible effects of surface disorder and defects on the theoretical rocking curves. Discrepancies present between theory and experiment mean that the values obtained for the surface model parameters should be regarded as only provisional. The effect upon rocking curves of varying the As surface coverage is then investigated. The experiment/theory comparison supports the 75% coverage of As observed using the STM, but a consideration of this RHEED data alone cannot exclude a 50% as coverage. Calculations employing unit cells containing surface defects suggest that such defects have very little effect upon sets of rocking curves. A consideration of the kinematic surface structure factor shows that surface disorder may markedly reduce the intensities of fractional-order diffraction features, yet have less effect upon whole-order features.