Carrier dynamics in Si nanocrystals in an SiO2 matrix investigated by transient light absorption

Open Access
Authors
Publication date 2013
Journal Physical Review B
Article number 155304
Volume | Issue number 88 | 15
Number of pages 9
Organisations
  • Faculty of Science (FNWI) - Van 't Hoff Institute for Molecular Sciences (HIMS)
  • Faculty of Science (FNWI) - Institute of Physics (IoP)
Abstract
We report on investigations of optical carrier generation in silicon nanocrystals embedded in an SiO2 matrix. Carrier relaxation and recombination processes are monitored by means of time-resolved induced absorption, using a conventional femtosecond pump-probe setup for samples containing different average sizes of nanocrystals (d(NC) = 2.5-5.5 nm). The electron-hole pairs generated by the pump pulse are probed by a second pulse over a broad spectral range (E-probe = 0.95-1.35 or 1.6-3.25 eV), by which information on excited states is obtained. Under the same excitation conditions, we observe that the induced absorption intensity in the near-infrared range is a factor of similar to 10 higher than in the visible range. To account for these observations, we model the spectral dependence of the induced absorption signal using an empirical sp(3)d(5)s* tight-binding technique, by which the spectrum can be well reproduced up to a certain threshold. For probe photon energies above this threshold (dependent on nanocrystal size), the induced absorption signal is found to feature a long-standing component, whereas the induced absorption signal for probe photon energies below this value vanishes within 0.5 ns. We explain this by self-trapping of excitons on surface-related states.
Document type Article
Language English
Published at https://doi.org/10.1103/PhysRevB.88.155304
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