AVS 47th International Symposium
    Surface Science Monday Sessions
       Session SS2+EL-MoA

Paper SS2+EL-MoA7
Lifetimes of Conduction Band States at Semiconductor Surfaces

Monday, October 2, 2000, 4:00 pm, Room 209

Session: Electronic Structure and Excitations
Presenter: Th. Fauster, University Erlangen, Germany
Authors: Th. Fauster, University Erlangen, Germany
M. Kutschera, University Erlangen, Germany
C. Kentsch, University Erlangen, Germany
M. Wiets, University Erlangen, Germany
I.L. Shumay, University Erlangen, Germany
M. Weinelt, University Erlangen, Germany
Correspondent: Click to Email
In time-resolved two-photon photoemission electrons are emitted after absorption of two photons. By a suitable delay between the two photons the lifetimes of conduction band states can be directly measured in pump-probe experiments. Using time-resolved two-photon photoemission we have studied several semiconductor surfaces. On the Si(100)-(2x1) surface several bulk and surface transitions with unoccupied intermediate states between the conduction band minimum and the vacuum energy are observed. Below the conduction band minimum we find a lifetime in the ps range, which we attribute to the unoccupied surface state. This unoccupied as well as the occupied surface state which originate from the silicon dangling bonds are clearly resolved within the same experiment. On epitaxial, metallic CoSi@sub 2@(111) films on a Si(111)-substrate three unoccupied states could be identified. Their lifetimes lie in the 10 fs range. Neither the lifetimes nor the energetic positions of those unoccupied states depend on the film thickness. On the SiC(0001)-(@sr@3x@sr@3)R30° surface the occupied and unoccupied Mott-Hubbard surface bands are observed. An asymmetric splitting relative to the Fermi level is found in agreement with recent theoretical calculations.