Angle-resolved photoemission studies of Ge(001)-(2×1)

Ge(001)-(2×{}1) surfaces prepared by either molecular-beam epitaxy or sputtering followed by annealing were studied with angle-resolved photoemission with use of synchrotron radiation in the photon-energy range of 14---45 eV. The surface electronic structure was found to be independent of preparation procedures. The upper bulk valence-band dispersions of Ge were determined from the Γ point to the X point along the [001] direction in the Brillouin zone; the results are in good agreement with the theoretical band dispersions of Chelikowsky and Cohen [Phys. Rev. B 14, 556 (1976)]. Three peaks were observed in the normal-emission spectra to show no dispersion over a wide photon-energy range. We will discuss if these peaks are derived from transitions involving surface states.