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Ultrafast-electron dynamics and recombination on the Ge(111)(2x1) pi-bonded surface

Ultraschnelle Elektronen-Dynamik und Rekombination an der Ge(111)(2x1) Pi-gebundenen Oberfläche
: Haight, R.; Baeumler, M.


Physical Review. B 46 (1992), No.3, pp.1543-1552
ISSN: 0163-1829
ISSN: 1098-0121
ISSN: 0556-2805
Journal Article
Fraunhofer IAF ()
electron-dynamics; Elektronendynamik; germanium; Oberfläche; Renormalisierung; renormalization; surface; ultrafast; ultraschnell

Angle-resolved laser-photoemission spectroscopy has been used to study the ultrafast-electron scattering and recombination processes on the Ge(111) pi-bonded (2 x 1) surface with subpicosecond time resolution. Electrons photoexcited into the bulk Ge conduction band scatter into the unoccupied surface antibonding pi band whose minimum is at the J point in the surface Brillouin zone. Rapid relaxation to the surface-band minimum is followed by a unique phonon-assisted process in which electrons recombine with bulk holes at the valence-band maximum, which we find to be the primary mechanism responsible for the decay of the transient pi population. Time-dependent measurements carried out at 300 and 120 K have been employed to determine the role of energetic phonons in the scattering processes. These processes are modeled with a set of rate equations, whose fits to the data yield scattering times used to determine a surface recombination velocity directly. Ultrafast surface-state hole dynami cs are observed, and a renormalization of the surface band gap is studied as a function of electron density. The pi-bonded states are fundamentally one dimensional in nature, and thus these results represent studies of band-gap renormalization in a one-dimensional system.