Electronic structure of Ge(111) and Ge(111): H from angle-resolved-photoemission measurements

Angle-resolved-photoemission measurements were made on the annealed (111) surface of germanium and on the same surface with adsorbed hydrogen. Spectra are presented for various values of ${\overrightarrow{\mathrm{k}}}_{\parallel }$, the wave-vector component parallel to the surface, for the $\left[1\mathrm{}\overline{1}0\right]$ and $\left[\overline{1}\overline{1}2\right]$ directions, and for photon energies of 16.85 and 21.22 eV. Two surface states at 0.8 and 1.4 eV below the top of the valence band were found in the spectra for the reconstructed Ge(111)-(8) surface. Both states showed only small changes in energy as a function of ${\overrightarrow{\mathrm{k}}}_{\parallel }$ but distinct intensity variations. Bulklike states were also found and are compared to $E\left({\overrightarrow{\mathrm{k}}}_{\parallel }\right)$ curves calculated with a pseudopotential method. The addition of hydrogen to the surface removed the reconstruction and drastically altered the photoemission spectra. A strong hydrogen-induced peak at an average binding energy of about 5 eV showed a similar dispersion to that calculated for Si(111): H by Pandey.