Electronic states of the clean Ge(001) surface near Fermi energy

Electronic states of the clean Ge(001) surface are studied by angle-resolved photoemission spectroscopy and standing wave observation with scanning tunneling microscopy. The bottom of the surface conduction band is 0.30.3em0exeV above the top of the valence band, and thermally filled with increasing temperature above 4700.3em0exK. Its dispersion in the direction perpendicular to the dimer axis is much larger than that in the Ge dimer-axis direction. The valence band top at Γ is a bulk state, and surface resonances exist near this point. These features are consistent with the band calculation based on the density functional theory for the c(4×2) surface.