Regensburg 2010 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 48: Surface dynamics I
O 48.6: Vortrag
Mittwoch, 24. März 2010, 11:45–12:00, H40
Relaxation dynamics and bulk-to-surface-recombination of hot electrons on Si(001) studied by two-photon photoemission — •Christian Eickhoff1,2 and Martin Weinelt1,2 — 1Max-Born-Institut, Max-Born-Straße 2a, 12489 Berlin, Germany — 2Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
We have studied the relaxation of hot carriers excited to the conduction band minimum (CBM) on the Si(001) surface. Two-photon photoemission combined with an electron analyzer equipped with a 2D-CCD-imaging detector allows us to follow the relaxation dynamics of photoexcited carriers in energy and momentum space simultaneously on a femtosecond timescale. With a pump fluence of 570 µ J/cm2 an electron density of ≈ 1018 cm−3 is created 1 eV above the CBM, leading to an ultrafast cooling of initially excited electrons within the laser pulse width of 70 fs. After 350 fs the hot carriers can be described by a Fermi-distribution with a temperature of several thousand Kelvin. This temperature initially decreases on a fast time scale of 1 ps to 350 K, the same time scale on which the observed intensity from the normally unoccupied surface state Ddown shows a strong increase. On a second time scale the remaining occupation in the CBM decreases within several hundred picoseconds. We conclude that electron-electron-scattering, which becomes important in semiconductors for excited carrier densities >1017 cm−3, is the main mechanism behind efficient bulk-to-surface-recombination in the first picosecond after excitation.