Dynamic effects in rheed from MBE grown GaAs(001) surfaces

Abstract Reflection high energy electron diffraction measurements of the intensity of (elastically) diffracted beams as a function of the incident angle have been carried out for an exactly oriented GaAs(001) surface, using a primary beam energy of 12.5 keV. Different surface reconstructions were prepared in-situ by molecular beam epitaxy and the measurements of the diffracted intensities were made at temperatures and As 2 -fluxes where these structures were stable. Results for the (0,0) beam in the [ 1 10], [110] and [010] azimuths are reported for the 2 × 4, 3 × 1 and c(4 × 4) structures and in addition for fractional and integral order beams for the 2 × 4 surface. In general, very large intensity variations (up to a factor of 10 4 ) are observed. The results are discussed in terms of diffraction processes involving primary Bragg, secondary Bragg and surface resonances, and refraction effects introduced by both bulk and surface “inner potentials” are included. The data cannot be explained using the kinematic approximation, but they are a consequence of multiple scattering events. The reconstructed surface layer appears to have a dominant influence. A complete analysis of the results would require full dynamical calculations based on realistic surface models, but they are not yet available. Finally, the significance of the results to recent observations of oscillations in diffracted intensity during thin film growth by molecular beam epitaxy is considered.