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-ra y photoemission spectroscopy (SXPS). The samples were grown lattice matched on GaAs(001) by metal organic vapor phase epitaxy. Immediately after growt h the surfaces were passivated by a P/As-double-layer cap and then transfer red to ultrahigh vacuum (UHV) analysis chambers for surface characterizatio n. Under UHV conditions an uncontaminated, well ordered (2X4) reconstructio n was reproducibly formed by thermal annealing for 10 min at. 460 degreesC. STM images with atomic resolution were obtained showing features typical f or the mixed-dimer (2X4) structure as known from InP(001). This interpretat ion 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 an y other reconstruction. The (2X4) mixed dimer structure thus represents the most III-rich (least P-rich) stable (001) surface.