PHOTOELECTRON AND AUGER-ELECTRON DIFFRACTION STUDIES OF A SULFUR-TERMINATED GAAS(001)-(2X6) SURFACE

Core-level X-ray photoelectron diffraction (XPD) and Auger electron di ffraction (AED) have been applied to investigate the sulfur-terminated GaAs(001)-(2 x 6) surface. No forward scattering peaks were found in the XPD pattern of S 2s emission, indicating that adsorbed S atoms for m a single layer on the GaAs substrate. In accordance with the zincble nde structure of GaAs, the AED patterns of Ga L3M45M45 and As L3M45M45 emission almost coincide with each other, if one of the emissions is rotated by 90 around the [001] direction. This fact suggests that the diffraction patterns mainly reflect the structure of the bulk GaAs cry stal. In order to investigate the surface structure, AED patterns in l arge polar angles were analyzed with single scattering cluster (SSC) c alculations. The best result was obtained with a model cluster where t he S-S bond length was set at 0.28 nm, 30% shorter than the correspond ing length of the ideal (1 x 1) structure, and the adsorption height w as set at 0.12-0.13 nm, 10% shorter than the ideal interlayer distance of GaAs(001) planes. These values are in good agreement with the resu lts of STM measurements. A modulation of the inter-dimer distance was also found, suggesting the existence of missing dimers. (C) 1998 Elsev ier Science B.V.