Time-resolved two-photon photoelectron spectroscopy of carrier dynamics on the Si(0 0 1)-(2 × 1) surface

The electron populations of the intrinsic surface unoccupied state (Ddown) and of the minimum of bulk conduction band (CBM) after fs-pulse excitation on the Si(0 0 1)-(2 × 1) surface were measured at two different excitation wavelengths (λex) by means of time-resolved two-photon photoelectron spectroscopy. The decay of populations of both states is faster for short-wavelength excitation at 377 nm than that at 754 nm, showing a prominent λex-dependent decay in sub-ns temporal domain. In this temporal domain, the populations of both Ddown and CBM are proportional with each other. The results show that the decay of Ddown population is governed by the de-population of bulk electrons near surface via a short lifetime at the Ddown state.