Electron spectroscopy and dynamics on the Ge(111):As 1×1 surface

Abstract

Femtosecond laser photoemission has been used to study the As derived empty surface bands on the Ge(111):As 1×1 surface. Electrons excited to energies well above the conduction band minimum of Ge are observed to populate valleys centered at the Γ ̄ and M̄ points of the surface Brillouin zone. The valley centered at M̄ is a surface resonance, located 0.3 eV above the Ge conduction band minimum and is transiently populated through an intervalley scattering process. At longer times the electrons are trapped in a normally unoccupied surface state at Γ ̄ which is located 0.2 eV below the conduction band minimum of bulk Ge. Our spectroscopic findings compare well with a many-body calculation for this system. Since the bottom of the surface band resides within the Ge bulk band gap, electrons remain trapped in this state at the surface for times approaching a nanosecond. The long lifetime is due to the lack of defect states within the surface band gap and thus only radiative recombination can remove electrons from the surface state. Our photoemission results also allowed for the extraction of the surface temperatures and the cooling rate of the excited electron population.