COMPOSITION AND STRUCTURE OF THE INP(100)-(1X1) AND INP(100)-(4X2) SURFACES

The composition and structure of an InP(100) surface in both the (1X1) and the reconstructed (4X2) phases, prepared by ion bombardment and annealing, have been examined by time-of-flight scattering and recoiling spectrometry (TOF-SARS) and low-energy electron diffraction (LEED). Time-of-flight spectra of scattered and recoiled neutrals plus ions were collected as a function of crystal azimuthal rotation angle delta and primary beam incident angle ct. Compositional analyses of the surfaces were obtained from 4 keV Ar+ scattering and recoiling spectra. Structural analyses of the phases were obtained from the azimuthal anisotropy of the scans and the features of the polar incident Lu-scans using 4 keV Ne+ scattering from In atoms and 4 keV Kr+ for recoiling of P atoms. These azimuthal delta-scans and incident cr-scans were simulated by means of a shadow cone focusing model and a modified version of the MARLOWE code, respectively. The totality of this data leads indubitably to a model in which every fourth In (0 $($) over bar$$ 11) row is missing, the In atoms are trimerized along the (011) azimuth, and the 2nd-layer P atoms exposed in the (0 $($) over bar$$ 11) troughs are dimerized. This In missing-row-trimer P dimer model (MRTD) is consistent with all of the data, is autocompensated, and has In intratrimer spacings of 3.65 +/- 0.20 Angstrom and P intradimer spacings of 2.95 +/- 0.20 Angstrom. The results of the simulations suggest that the two end In atoms of the trimers are relaxed downward by a minimum of 0.15 Angstrom. Two other models were considered: (1) An In missing-row (MR) model without trimers or dimers in which every fourth In (0 $($) over bar$$ 11) row is missing. (2) an In missing-row-dimer (MRD) model, similar to that proposed for the GaAs (4X2) structure, in which every fourth In (011) row is missing and In dimers form along (011). These MR and MRD models are inconsistent with large portions of the experimental data and the simulations.