Single dot optical spectroscopy of silicon nanocrystals: low temperature measurements

Single dot spectroscopy allows studying properties of a single nanocrystal avoiding inhomogeneous broadening of the emission band. Here, data obtained by this technique for Si nanocrystals fabricated by electron beam lithography, plasma etching and subsequent size-reduction by oxidation are presented. First, blinking (on-off intermittence) of the luminescence was observed for most individual nanocrystals, although some exhibited relatively stable luminescence. As a result of the quantum confinement effect spectra with different emission wavelengths for different nanocrystals were recorded. While at room temperature the full width at half-maximum of the nanocrystal emission peaks was measured to be ∼100-150 meV, at 80 K the linewidth for some dots appeared to be about ∼25 meV only. The observed temperature dependence of the homogeneous linewidth may lead to an understanding of the exciton-phonon interaction in indirect band-gap quantum dots.