Sulfur-adsorbed GaAs(001) surface studied by X-ray absorption near edge structure, X-ray standing waves and X-ray diffraction

Sulfur-adsorbed GaAs(001)-(2 x 6) surface was studied by X-ray absorption near edge structure (XANES), X-ray standing waves (XSW) and X-ray diffraction. Strong polarization dependence in S K-edge XANES spectra revealed that most of the sulfur atoms are located in the top layer and form Ga-S-Ga bridge bonds. The XSW results showed the three-dimensional adsorption site of the sulfur atoms to be a bridge site. The sulfur atomic layer was determined to be ca 1.1 Angstrom above the ideal second Ga layer. The crystal truncation rod (CTR) scattering profile near the (002) reflection of the GaAs substrate could not be explained by the unrelaxed Ga layer model. We propose that lattice distortion of the subsurface region is induced by sulfur adsorption. (C) 1997 Elsevier Science B.V.