Femtosecond studies of plasma formation in crystalline and amorphous silicon

Waldemar Kuett; Anton Esser; Klaus Seibert; Uli Lemmer; Heinrich Kurz

doi:10.1117/12.20333

1 August 1990 Femtosecond studies of plasma formation in crystalline and amorphous silicon

Waldemar Kuett, Anton Esser, Klaus Seibert, Uli Lemmer, Heinrich Kurz

Proceedings Volume 1268, Applications of Ultrashort Laser Pulses in Science and Technology; (1990) https://doi.org/10.1117/12.20333
Event: The International Congress on Optical Science and Engineering, 1990, The Hague, Netherlands

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.

Citation Download Citation

Waldemar Kuett, Anton Esser, Klaus Seibert, Uli Lemmer, and Heinrich Kurz "Femtosecond studies of plasma formation in crystalline and amorphous silicon", Proc. SPIE 1268, Applications of Ultrashort Laser Pulses in Science and Technology, (1 August 1990); https://doi.org/10.1117/12.20333

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