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The transport properties, particularly free carrier density and mobility, of SiC are usually determined by the Hall effect. Raman spectroscopy has been shown to yield transport parameters similar to the Hall effect. The analysis of the longitudinal optical plasmon coupled (LOPC) modes in doped SiC provides such information. In the case of damped plasmons in n-type 4H–SiC, changes in the carrier concentration result in a frequency shift of the LOPC mode, which appears close to the A1(LO) phonon mode. The validity of this approach for different free carrier concentrations (plasma frequencies) and mobilities (plasmon damping constants) is analyzed. The theoretical results obtained show that reliable estimation of the free carrier density can be obtained from the frequency shift of the LOPC mode for low carrier concentrations. At such a carrier concentration a reliable correlation between the Raman shift of the LOPC mode and the plasma frequency is established, without noticeable influence of the plasmon damping constant. However, when the free electron concentration increases, a non-negligible influence of the plasmon damping constant on the Raman frequency shift of the LPOC mode is observed. Therefore reliable transport data can only be obtained by a full line-shape analysis. These results are confirmed by the experimental results obtained on n-type 4H–SiC bulk samples with free electron concentration between 1×1017 and 5×1018 cm−3. © 2001 American Institute of Physics.

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Raman spectroscopy provides nondestructive information about nanoscaled semiconductors by modeling the phonon confinement effect. However, the Raman spectrum is also sensitive to the temperature, which can mix with the size effects borrowing the interpretation of the Raman spectrum. We present an analysis of the Raman spectra of Si nanowires (NWs). The influence of the excitation conditions and the temperature increase in the NWs are discussed. The interpretation of the data is supported by the calculation of the temperature inside the NWs with different diameters.

International audienceThe Raman spectrum of Si nanowires (NWs) is a matter of controversy. Usually, the one-phonon band appears broadened and shifted. This behaviour is interpreted in terms of phonon confinement; however, similar effects are observed for NWs with dimensions for which phonon confinement does not play any relevant role. In this context, the temperature increase induced by the laser beam is recognized to play a capital role in the shape of the spectrum. The analysis of the Raman spectrum, under the influence of the heating induced by the laser beam, is strongly dependent on the excitation conditions and the properties of the NWs. We present herein an analysis of the Raman spectrum of Si NWs based on a study of the interaction between the laser beam and the NWs, for both ensembles of NWs and individual NWs, taking account of the temperature increase in the NWs under the focused laser beam and the dimensions of the NWs

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The luminescence emission of structures containing Ge nanocrystals embedded in a dielectric matrix obtained by dry and wet oxidation of polycrystalline SiGe layers has been studied as a function of the oxidation time and initial SiGe layer thickness. A clear relationship between the intensity of the luminescence, the structure of the sample, the formation of Ge nanocrystals and the oxidation process parameters that allows us to select the appropriate process conditions to get the most efficient emission has been established. The evolution of the composition and thickness of the growing oxides and the remaining SiGe layer during the oxidation processes has been characterized using Raman spectroscopy, x-ray diffraction, Fourier-transform infrared spectroscopy, Rutherford backscattering spectrometry and transmission electron microscopy. For dry oxidation, the luminescence appears suddenly, regardless of the initial SiGe layer thickness, when all the Si of the SiGe has been oxidized and the remaining layer of the segregated Ge starts to be oxidized forming Ge nanocrystals. Luminescence is observed as long as Ge nanocrystals are present. For wet oxidation, the luminescence appears from the first stages of the oxidation, and is related to the formation of Ge-rich nanoclusters trapped in the mixed (Si and Ge) growing oxide. A sharp increase of the luminescence intensity for long oxidation times is also observed, due to the formation of Ge nanocrystals by the oxidation of the layer of segregated Ge. For both processes the luminescence is quenched when the oxidation time is long enough to cause the full oxidation of the Ge nanocrystals. The intensity of the luminescence in the dry oxidized samples is about ten times higher than in the wet oxidized ones for equal initial thickness of the SiGe layer.

High gain and high saturation output power silicon-based semiconductor optical amplifiers (SOAs) are essential elements in future large-scale silicon photonic integrated circuits (PICs) to compensate for the excess power penalties that are introduced by large numbers of passive components. We present here, for the first time, to the best of our knowledge, an O-band quantum-dot (QD) SOA that is directly grown on a complementary metal-oxide-semiconductor compatible on-axis (001) silicon substrate. The QD-SOA demonstrates a > 100 nm gain bandwidth with an on-chip gain larger than 20 dB at 20 °C. A gain maxima of 39 dB occurs at the ground state peak wavelength with a 23 dBm saturation output power. P-modulation doping in the dot spacer layers is important to achieve higher gains (>20 dB) at high temperature (70 °C) with a 21 nm bandwidth. A fiber-to-fiber noise figure as low as 6.1 dB and a wall plug efficiency as high as 19.7% are also shown. The performance shows that the Si-based QD-SOAs can be important for Si PICs and employed under uncooled scenarios.