We investigated the scattering dynamics of hot electrons at the atomically well-defined In-rich (2 x 4)reconstructed InP(100) surface in the presence of different surface states. Using energy- and time-resolved femtosecond two-photon photoemission spectroscopy, we determined the electron transfer between three-dimensional bulk states and the two-dimensional surface state C2, located high above the conduction band minimum (CBM) avoiding energetic overlap with relaxed bulk electrons. At excitation energies, where C2 was populated through hot bulk electrons, relaxing towards the CBM, we found evidence that the energy loss rate of the photoexcited electron distribution is mostly determined by inelastic electron-phonon scattering between bulk states. This was confirmed by measurements repeated after quenching the surface states with oxygen. For resonant photoexcitation, on the other hand, we measured a time constant of iota(fast) = 20 fs for the depopulation of C2, showing that electron-phonon scattering between bulk and surface states might have direct consequence on ultrafast relaxation dynamics for materials with a high surface-to-bulk ratio.
Ultrafast electron scattering from surface to bulk states at the InP(100) surface