Valence band photoemission from in-situ grown GaAs(100)-c(4 × 4) * ) P. Jiˇ r´ ıˇ cek, M. Cukr, I. Bartoˇ s Institute of Physics, Acad. Sci. CR, 162 53 Praha, Czech Republic M. Adell Department of Experimental Physics, Chalmers University of Technology, SE–412 96, G˜ oteborg, Sweden T. Strasser, W. Schattke Institut f¨ ur Theoretische Physik,Christian-Albrechts-Universit¨at, D–24098, Kiel, Germany Received 22 November 2005 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 pre- pared 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 nondis- persing 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 22eV 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. PACS : 73.20.At, 73.61.Ey Key words : GaAs(100)-c(4 × 4), surface states, band structure, structure plot Introduction GaAs has become an interesting material in basic research. The (110) surface is the best studied plane of GaAs [1–3] both experimentally and theoretically. How- ever, for electronic devices the (100) plane is usually applied. For this reason the (100) surface has been studied during the recent years. Molecular beam epitaxy (MBE) is mostly used for preparation of this surface because of its ability to control surface stoichiometry in a wide range. The (100) * ) Presented at the X-th Symposium on Suface Physics, Prague, Czech Republic, July 11–15, 2005. Czechoslovak Journal of Physics, Vol. 56 (2006), No. 1 21