Atomic structure and composition of the (2×4) reconstruction of InGaP(001)

Abstract

In this study scanning tunneling microscopy (STM), soft x-ray photoemission spectroscopy (SXPS), and reflectance anisotropy spectroscopy were used to investigate the microscopic structure of (2×4) reconstructed InGaP(001) surfaces. The samples were grown lattice matched on GaAs(001) by metalorganic vapor phase epitaxy. Immediately after growth the surfaces were passivated by a thick amorphous cap consisting of a P/As double layer and then transferred to ultrahigh vacuum (UHV) analysis chambers either equipped with STM or connected to the BESSY synchrotron radiation source for photoemission experiments. Thermal desorption of the As/P capping layer at 460 °C under UHV conditions leads reproducibly to the formation of a III-rich (2×4) reconstruction, the more P-rich (2×1) could not be obtained. The low energy electron diffraction image shows a clear (2×4) pattern with sharp integer-order and fractional-order spots. STM images show rows along the [1̄10] direction with fourfold separation in the [110] direction, similar to the (2×4) reconstruction of InP(001). SXPS spectra of the In 4d/Ga 3d and P 2p core levels demonstrate that this surface may consist of a mixed-dimer structure analogous to the one found on InP(001) and GaP(001) (2×4). Further annealing of the sample to higher temperatures degrades the surface without producing another reconstruction. The (2×4) reconstruction thus represents the most III-rich (least P-rich) stable surface for InGaP(001).