Berlin 2005 – wissenschaftliches Programm
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O: Oberflächenphysik
O 15: Postersitzung (Adsorption an Oberfl
ächen, Epitaxie und Wachstum, Organische Dünnschichten, Oxide und Isolatoren, Rastersondentechniken, Zeitaufgelöste Spektroskopie, Methoden)
O 15.71: Poster
Freitag, 4. März 2005, 17:00–20:00, Poster TU D
Charge Carrier Dynamics at Silicon surfaces: A Time-Resolved Photoemission Study with Combined Laser and Synchrotron Radiation. — •Tatjana Gießel1, David Bröcker1, Helena Prima Garcia1, Ramona Weber1, Martin Weinelt1,2, and Wolf Widdra3 — 1Max-Born-Institut, Berlin, Germany — 2Freie Universität, Berlin, Germany — 3Martin Luther Universität, Halle, Germany
Charge carrier dynamics at the Si(100) surface and for thin oxide layers on Si(100) have been studied by probing the time-dependent surface photovoltage (SPV). Electron-hole pairs are excited in the near-surface region by femtosecond lasers pulses and the subsequent dynamics of charge carrier recombination is determined by time-resolved Si 2p core-level photoemission using synchrotron radiation. For laser fluences up to 60 µ J/cm2 the observed non-exponential decay of the SPV can be described within a model based on thermionic emission. For higher laser fluences up to 60 mJ/cm2 an oscillation of the SPV in time is observed. A fast drop of the SPV within 100 ps is followed by a slow increase reaching its maximum at several 100 nanoseconds. An even slower decay in the microsecond range then restores the primary SPV. The decay time of the initial fast drop of the SPV decreases with increasing sample temperature, which suggests a phonon mediated charge-carrier recombination-process. The subsequent SPV dynamics on the time scale of hundreds of nanoseconds to microseconds are assigned to diffusion-limited processes.