QUANTITATIVE-ANALYSES OF RHEED PATTERNS FROM MBE GROWN GAAS(001)-2X4 SURFACES

A multislice formalism of Cowley and Moodie [Acta Crystallogr. 10 (1957) 609] with a recently developed edge-patching method has been applied to quantitative analyses of RHEED patterns from MBE grown GaAs(001)-2 x 4 surfaces. The analyses are based on the ordering of visually estimated spot intensities of several observed RHEED patterns from the GaAs(001)-2 x 4 surfaces. The surface structure is proved to be a dimerized vacant 2 x 4 reconstruction missing one dimer of every four along the [110] direction, which is consistent with previous STM observations. The relaxation of the top layer is found to be about delta = + 8.0% (0.113 angstrom). The results give an overall Debye-Waller factor of B = 0.35 angstrom2 and a crystal absorption of alpha = 0.1 for the conditions at which the observed RHEED patterns were acquired. The effects of dimer twist on the intensities of RHEED patterns are briefly assessed. This indicates that twist of dimers on the GaAs(001)-2 x 4 surface is unlikely. Errors involved in the calculations are also discussed.