IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Wednesday Sessions
       Session SS3-WeA

Paper SS3-WeA3
Lifetimes of Surface States at Si(001) Surfaces

Wednesday, October 31, 2001, 2:40 pm, Room 122

Session: Electronic Structure I
Presenter: M. Weinelt, Universität Erlangen-Nürnberg, Germany
Authors: M. Weinelt, Universität Erlangen-Nürnberg, Germany
M. Kutschera, Universität Erlangen-Nürnberg, Germany
C. Kentsch, Universität Erlangen-Nürnberg, Germany
Ch. Orth, Universität Erlangen-Nürnberg, Germany
Th. Fauster, Universität Erlangen-Nürnberg, Germany
Correspondent: Click to Email
With ultrafast two-photon photoemission spectroscopy the temporal evolution of an excited electronic system can be studied on the femtosecond time scale. A pump pulse excites electrons to distinct intermediate states while a second time-delayed pulse probes the evolving population dynamics. This allows to determine lifetimes of conduction bands and unoccupied dangling-bond states on semiconductor surfaces directly in the time domain. Using time-resolved two-photon photoemission we have studied the c(4 x 2) and (2 x 1) reconstructions of the Si(100) surface. Several bulk and surface transitions involving unoccupied intermediate states below the vacuum energy are identified. In particular, the surface band gap at the center of the surface Brillouin zone, i.e., the gap between occupied and unoccupied dangling-bond states is determined to 0.96 ± 0.05 eV. The unoccupied dangling-bond state shows a rich dynamic ranging from fs to more than 100 ps. Population and decay are dominated by electron-phonon scattering which couples bulk and surface states. The decay rate is strongly influenced by surface defects in the band gap.