Analysis of low-energy electron diffraction and angle-resolved photoemission from InP(110)-p(1 × 1)-Sb (1 ML)

The deposition of Sb on InP(110) at room temperature produces a stable, ordered, saturated adsorbate structure at a coverage of approximately one monolayer (1 ML, i.e., one Sb for each In and P surface species). An analysis of the atomic geometry of this InP(110)-p(1 × 1)-Sb(1 ML) overlayer system was performed by the comparison of dynamical calculations of elastic low-energy electron diffraction (ELEED) intensities with those measured at T = 110 K. A relativistic model embodying energy-dependent Hara exchange was utilized to calculate the electron scattering from the In, Sb and P ion cores because both relativistic effects and energy-dependent exchange have been found previously to be important in the analysis of ELEED intensity data from In and Sb containing compounds. On the basis of prior results for GaAs(110)-p(1 × 1)-Sb and of total-energy minimization calculations the structural search was confined to models in which the Sb adsorbates occupy inequivalent sites corresponding to the top layer In and P species on nearly unreconstructed InP(110). The quality of the description of the measured ELEED intensities by the model geometries was evaluated using the X-ray (R_X) and integrated intensity (R_I) R-factors. Two comparable minimal R_X structures are found corresponding to perpendicular displacements of Δ_1,⊥ = 0.25 A ̊ and 0.75 A ̊, respectively, of the two inequivalent surface Sb species. In both structures the SbSb bond lengths are at nearly the value characteristic of bulk Sb (i.e., 2.87 Å) but the SbP bond length is anomalously small (i.e., 2.1 Å) for the Δ_1,⊥ = 0.75 A ̊ structure. Utilization of these structures to calculate the surface state eigenvalue spectrum reveals that both of them provide a satisfactory description of the surface states extracted from angle-resolved valence-electron photoemission.