The atomic structure of the 2 x 1 reconstructed (001) surface, prepared under optimum molecular beam epitaxy conditions, was determined by means of  in situ  grazing-incidence X-ray diffraction measurements. It was found that the structure involved only 2 dimers in the upper As layer, in agreement with recent scanning tunnelling microscopic data. In addition, the presence of an As dimer in the third layer (due to a missing Ga row in the second layer) was confirmed. Full agreement with first-principles total-energy calculations was obtained for atomic displacements down to the fourth atomic layer below the surface. A quantitative line-shape analysis, using a diffuse scattering formalism, demonstrated the effect upon the intensity distribution of the most frequent faults in reconstruction propagation.

Y.Garreau, M.Sauvage-Simkin, N.Jedrecy, R.Pinchaux, M.B.Veron: Physical Review B, 1996, 54[24], 17638-46