Quality factor of Si-based photonic crystal L3 nanocavities probed with an internal source.

We have investigated the quality factors of silicon-based photonic crystal nanocavities using the photoluminescence of a single layer of Ge/Si self-assembled islands as an internal source. We focus on membrane-type L3 elongated cavities with or without their lateral edge air holes shifted in position. The photoluminescence measurements are performed at room temperature. We show that the quality factor of the fundamental mode observed at a normalized frequency u = a/lambda~_ 0.25 is strongly dependent on the incident pump power. This dependence is associated with the free-carrier absorption of the photogenerated carriers. The slope of the quality factor vs. incident pump power gives access to the carrier recombination dynamics in these Si-based nanocavities. The measurements indicate that the carrier dynamics is controlled by nonradiative recombination associated with surface recombinations. A surface recombination velocity of 4.8 x 10(4) cm/s is deduced from the experiments. The spectral red-shift of the cavity modes as a function of incident pump power is correlated to the temperature rise due to thermo-optic effects. The measured temperature rise, which can reach 190 K, is correlated to the value estimated by a thermal analysis.

Inelastic electron scattering observation using energy filtered transmission electron microscopy for silicon -- germanium nanostructures imaging.

This paper presents a new technique using energy filtered TEM (EFTEM) for inelastic electron scattering contrast imaging of Germanium distribution in Si-SiGe nanostructures. Comparing electron energy loss spectra (EELS) obtained in both SiGe and Si single crystals, we found a spectrum area strongly sensitive to the presence of Ge in the range [50-100 eV]. In this energy loss window, EELS spectrum shows a smooth steeply shaped background strongly depending on Ge concentration. Germanium mapping inside SiGe can thus be performed through imaging of the EELS background slope variation, obtained by processing the ratio of two energy filtered TEM images, respectively, acquired at 90 and 60 eV. This technique gives contrasted images strongly similar to those obtained using STEM Z-contrast, but presenting some advantages: elastic interaction (diffraction) is eliminated, and contrast is insensitive to polycrystalline grains orientation or specimen thickness. Moreover, since the extracted signal is a spectral signature (inelastic energy loss) we demonstrate that it can be used for observation and quantification of Ge concentration depth profile of SiGe buried layers.