Ultrafast time-resolved spectroscopy of Si nanocrystals embedded in SiO2 matrix

In this work, we study theoretically the resonant coupling between longitudinal optical surface vibrations of Si-OH and/or Si-O-Si and electron and hole states in the silicon nanocrystals (Si NCs) within light emitting porous Si (PSi) thin films in the framework of the Fröhlich interaction. The results of this analysis are compared with experimental results, which show considerable enhancement and a redshift of the photoluminescence (PL) spectrum of a fresh as-grown PSi thin film after prolonged laser irradiation or after aging in air. These effects coincide with the formation of Si-OH and Si-O-Si bonds on the surface of PSi. The redshift of the PL spectrum is due to the pinning of the bandgap of the light emitting Si NCs, as both oxidation via laser irradiation in air and aging in air introduce energy states in the Si NC band gaps. According to the theoretical analysis, the PL enhancement is assigned to inhibition of nonradiative channels rather than to an enhancement of radiative channels in the Si NCs within the PSi film, due to a strong coupling of the surface Si-OH and/or Si-O-Si vibrational modes to the electronic sublevels in the Si NCs within the PSi layer.

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Hot-phonon-induced indirect absorption in silicon nanocrystals

Kozák¹,

Kořínek²,

Trojánek³

et al. 2013

Journal of Applied Physics

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We studied the nonlinear transient absorption dynamics in silicon nanocrystals/SiO2 superlattices. A different dependence of the measured dynamics on excitation intensity was observed depending on the relative position of the probe photon energy and the absorption edge of nanocrystals. At low photon energies, the dynamics changed with excitation fluence and the signal was ascribed to excited state absorption. However, at photon energies above the absorption edge, the phonon enhancement of indirect absorption prevails over excited state absorption what is reflected in excitation fluence independent dynamics of transient absorption.

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Ultrafast time-resolved spectroscopy of Si nanocrystals embedded in SiO2 matrix

Cited by 4 publications

References 23 publications

Quantum size-dependent luminescence and nonlinear optical properties of silicon quantum dots/SiO2 multilayer

Quantum size-dependent luminescence and nonlinear optical properties of silicon quantum dots/SiO2 multilayer

Role of surface vibration modes in Si nanocrystals within light emitting porous Si at the strong confinement regime

Hot-phonon-induced indirect absorption in silicon nanocrystals

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