Valence band photoemission from in-situ grown GaAs(100)-c(4 × 4)

The electron structure of GaAs(100)-c(4 × 4) has been studied by means of angular-resolved photoelectron spectroscopy for photon energies (20–40) eV. The sample was prepared by molecular beam epitaxy in-situ at the BL41 beamline of the MAX I storage ring of the Max-lab in Lund. Photon energy variation helped in separating dispersing bulk features from nondispersing surface features in the energy distribution curves recorded at normal emission. Two sets of peaks were related to bulk transitions from the two topmost E(k _⊥) branches of the valence band of GaAs and one more set came from the surface state in the center of the 2D Brillouin zone. Good agreement was found between experimental bulk dispersion branches and theoretical calculations based on realistic final state dispersion. The surface state peak, hardly visible at 20 and 22 eV photon excitations, gets clearly enhanced at higher excitation energies. In contrast to earlier measurements of this kind, two major differences have been found: (i) clearly developed surface state peak just below the top of the v alence band, (ii) absence of a large peak in the electron energy distribution at around −6.5eV below the valence band top. Presented at the X-th Symposium on Suface Physics, Prague, Czech Republic, July 11–15, 2005.