STRUCTURAL DETERMINATION OF THE S-PASSIVATED INP(100)-(1X1) SURFACE BY DYNAMICAL LOW-ENERGY ELECTRON-DIFFRACTION ANALYSIS

We have determined the optimum geometry of the S-passivated InP(100)-(1X1) surface by dynamical low-energy electron-diffraction analysis. S atoms bond to In by occupying the bridge site that continues the zinc-blende stacking 'sequence of the substrate. Other potential high-symmetry adsorption sites (atop, antibridge, and hollow) can be clearly ruled out. The overlayer-substrate interlayer spacing is found to be 1.445+/-0.033 Angstrom, and the topmost substrate interlayer spacing is found to be 1.465+/-0.035 Angstrom. Both values are close to the bulk interlayer spacing of 1.468 Angstrom. We also have investigated the S coverage within the framework of the average t-matrix approximation, and our results favor a full monolayer. However, the coverage could be as low as 0.77 monolayer when the uncertainty is taken into account. The optimum geometry of the S-passivated surface is consistent with sp(3)-hybridized S and In forming predominantly covalent bonds, which has important implications with regard to the passivation mechanism.