Angle-resolved photoemission study of two phases of the GaAs(100)-c(4x4) surface

We prepared two surface phases of the Ga(001)-c(4x4) reconstruction (alpha, beta) by molecular beam epitaxy (MBE) using As-4 and As-2 molecular beams and examined the surfaces by angle-resolved ultraviolet photoelectron spectroscopy (UPS) and core level photoelectron spectroscopy with the synchrotron radiation as the excitation source. It is demonstrated that the photoelectron spectroscopy can distinguish between the phases. Appearance of intensive surface state 0.5 eV below the top of the valence band at lower energies is linked to the presence of the beta-phases on the surface while in the a-phase spectra the peak is missing. Both As 3d and Ga 3d photoelectron lines show substantial differences between the phases in line shapes as well as in their deconvoluted components. The 3d data are in agreement with different surface composition and atomic structure of both phases.