Multivalley Electron Population Dynamics on the Ge(111):As Surface

Electrons excited to energies well above the conduction band minimum of Ge are observed to populate valleys centered at the $\overline{\gamma }$ and $\overline{M}$ points of the Brillouin zone on the As-terminated Ge(111) surface. The valley centered at $\overline{M}$ is a surface resonance, located 0.3 eV above the Ge conduction band minimum. The subpicosecond population dynamics are followed directly with harmonic laser photoemission. The time evolution of the excited electron gas temperature was measured and a cooling rate was determined.