ORDERING OF SULFUR INTERLAYER IN MOLECULAR-BEAM EPITAXY-GROWN SRF2,/S/GAAS(111)A AND SRF2,/S/GAAS(111)B

SrF2 films are epitaxially grown on sulfur-passivated GaAs(111)A and GaAs(111)B at a substrate temperature of 430 degrees C. The epitaxial relations of these SrF2/S/GaAs{111} systems are type A. The position and the ordering degree of sulfur interlayer were investigated by soft X-ray standing-wave (soft-XSW) triangulation studies. By the SrF2 epitaxial growth, the ordering degrees of the sulfur interlayer are reduced. The in-plane distribution of the sulfur interlayer is more disordered than the surface normal one, indicating that sulfur atoms buried under the SrF2 epitaxial layers grown at 430 degrees C do not homogeneously occupy identical in-plane sites.