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Proceedings Paper

Femtosecond studies of plasma formation in crystalline and amorphous silicon
Author(s): Waldemar Kuett; Anton Esser; Klaus Seibert; Uli Lemmer; Heinrich Kurz
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Paper Abstract

Transient pump-probe reflectivity measurements are performed on crystalline and amorphous Silicon samples with 50 fs optical pulses at 2 eV. The excited carrier densities range from 1017cm3 up to a few 1021cm3. In both cases the reflectivity signal is dominated by a Drude-like carrier response. Crystalline Silicon shows a distinct subpicosecond feature due to the cooling of the optically excited hot carriers with a time constant of 200-300 fs. Diffusion and Auger-recombination come into play at higher carrier densities. A superlinear increase of instant reflectivity signal with excitation fluence is due to two-photon absorption (TPA) with a TPA-coeffiecient f:37+-5 cm/GW. In amorphous Silicon the TPA process is not observable. The recovery of the induced negative reflectivity changes is dominated by trapping into bandtail and defect states at lower carrier densities. At higher densities a non-radiative recombination process dominates the relaxation of free carriers in both materials. Comparison with crystalline Silicon clearly demonstrates the enhancement of the Auger-recombination process in disordered materials by more than an order of magnitude.

Paper Details

Date Published: 1 August 1990
PDF: 12 pages
Proc. SPIE 1268, Applications of Ultrashort Laser Pulses in Science and Technology, (1 August 1990); doi: 10.1117/12.20333
Show Author Affiliations
Waldemar Kuett, RWTH Aachen (Germany)
Anton Esser, RWTH Aachen (Japan)
Klaus Seibert, RWTH Aachen (Germany)
Uli Lemmer, RWTH Aachen (Germany)
Heinrich Kurz, RWTH Aachen (Germany)

Published in SPIE Proceedings Vol. 1268:
Applications of Ultrashort Laser Pulses in Science and Technology
Andre Antonetti, Editor(s)

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