Angle-resolved photoelectron spectroscopy investigation of intrinsic surface states on the Ge(001)-(2 × 1) reconstructed surface

Synchrotron-radiation-excited angle-resolved photoelectron spectra of the Ge(001)-(2 × 1) reconstructed surface reveal two surface states 0.6 and 1.3 eV below the bulk valence-band maximum at the $\Gamma$ point of the surface Brillouin zone. These two states are similar to those observed previously for Si(001) and GaAs(001) surfaces. The dispersion of the Ge bands with $k_{\parallel }$ is qualitatively in agreement with the calculations of Chadi using his asymmetric dimer model for Si(001)-(2 × 1).