Electonic Structure of Si(100) at high Laser Intensities

First laser-synchrotron pump-probe experiments in the low-α mode at BESSY demonstrate a time-resolution below 20 ps. Upon laser excitation close to the damage threshold (70 mJ/cm²) we observe reversibel changes in the photoemission spectra in both the valence band and core level region. (The damge threshold was found at 200mJ/cm²). The observed changes can be assigned to the Si(100) surface and bulk, respectively.

The Si(100) surface

Valence band
Changes in the valence band region are clearly distinguishable from surface photovoltage effects and are interpreted in terms of bulk band gap renormalization and depopulation of the D_up surface state.

Si 2p core level
Regarding the Si 2p core level region a significant broadening of the surface core level shifted components was observed, while the width of the bulk components remained nearly the same. A uniform temperature rise (as a trivial explaination of this behavior) can be excluded. We interpret the asymmetric broadening of the Si 2p core level in terms of a reversibel defect formation associated with the depopulation of the D_up surface state observed in the valence band spectra.

Si 2p analysis according to Yeom et al., Phys Rev. B 67, 073306 (2003)

Asymmetric broadening of the Si 2p core level upon laser excitation