Surface structure of ordered InGaP(001):: The (2x4) reconstruction

In this study the atomic structure of (2X4) reconstructed In0.48Ga0.52P(001) surfaces is analyzed by scanning tunneling microscopy (STM) and soft x-ray photoemission spectroscopy (SXPS). The samples were grown lattice matched on GaAs(001) by metal organic vapor phase epitaxy. Immediately after growth the surfaces were passivated by a P/As-double-layer cap and then transferred to ultrahigh vacuum (UHV) analysis chambers for surface characterization. Under UHV conditions an uncontaminated, well ordered (2X4) reconstruction was reproducibly formed by thermal annealing for 10 min at. 460 degreesC. STM images with atomic resolution were obtained showing features typical for the mixed-dimer (2X4) structure as known from InP(001). This interpretation is substantiated by the appearance of two surface core level components in the SXPS spectra of In 4d and Ga 3d plus one in the P 2p emission line, as expected for the mixed-dimer structure. Further annealing of the sample to higher temperatures under UHV degrades the surface without producing any other reconstruction. The (2X4) mixed dimer structure thus represents the most III-rich (least P-rich) stable (001) surface.