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We report a spectroscopic study about the energy transfer mechanism among silicon nanoparticles (Si-np), both amorphous and crystalline, and Er ions in a silicon dioxide matrix. From infrared spectroscopic analysis, we have determined that the physics of the transfer mechanism does not depend on the Si-np nature, finding a fast (<200 ns) energy transfer in both cases, while the amorphous nanoclusters reveal a larger transfer efficiency than the nanocrystals. Moreover, the detailed spectroscopic results in the visible range here reported are essential to understand the physics behind the sensitization effect, whose knowledge assumes a crucial role to enhance the transfer rate and possibly employing the material in optical amplifier devices. Joining the experimental data, performed with pulsed and continuous-wave excitation, we develop a model in which the internal intraband recombination within Si-np is competitive with the transfer process via an Auger electron-'recycling' effect. Posing a different light on some detrimental mechanism such as Auger processes, our findings clearly recast the role of Si-np in the sensitization scheme, where they are able to excite very efficiently ions in close proximity to their surface. [ABSTRACT FROM AUTHOR]

Hydrogenated nanocrystalline silicon carbide were grown at various deposition temperatures Td from 200 to 600 °C by means of reactive magnetron sputtering in a plasma of 80% H2 and 20% Ar mixture. A detailed investigation of the structural, compositional, phase nature, and morphology was carried out by complementary sophisticated techniques, such as Fourier transform infrared spectroscopy, x-ray diffraction (XRD), Rutherford backscattering, nuclear reaction, and elastic recoil detection analysis techniques, in addition to conventional and high-resolution transmission electron microscopy (HRTEM) observations. A crystallization onset with a fraction of 35% was observed for Td=300 °C, which improved to 80% for Td=600 °C, reflected by an increasing density of the SiC nanocrystals which kept an average size of about 5 nm. The observed fiber textures present <102> and <11ℓ> texture components, with ℓ larger than 2, while SiC nanocrystals elongated along the [111] direction are also evidenced. These latter are supported by the careful analyses of the HRTEM images which show evidence of faulted growing cubic SiC, as the origin of the very close hexagonal 6H–SiC structure taken into account in the XRD refinement. These various features were found quite consistent with the optical properties of the layers, and, in particular, the evolutions of both optical gap and static refractive index. [ABSTRACT FROM AUTHOR]

Textured silicon thin films are deposited by reactive magnetron sputtering in hydrogen-rich plasma on (100)-Si and amorphous SiO2 substrates. We quantitatively determine, combining x-ray texture analysis, x-ray reflectivity, transmission electron microscopy, atomic force microscopy measurements, and Raman and Fourier transform infrared spectroscopy analyses, the structure (cell parameter and mean electron density) and microstructure (crystalline fraction, preferred orientations, anisotropic crystallite sizes, thicknesses, etc.) of these films. For both kinds of substrates, no perfect <111> orientation is observed whereas a systematic elongation of the anisotropic Si crystallites along one [111] direction is present. A small elongation of the Si cell parameter of the nanocrystals is found without internal stress. With the substrate to target distance, the crystalline fraction and mean electron density show an opposite behavior to that of the film porosity. The former increases and the latter decreases, and are correlated to the texture evolution. Preferred orientations are observed with texture strengths around two to three times a random distribution, with a tendency to achieve lower strengths for films grown on SiO2 substrates. The texture components are evolving with the substrate to target distance, with <110> and (ℓ larger than 2) orientations favored for smaller and larger distances, respectively. All these microstructural properties are correlated with their optical properties and more particularly to their refractive index and their optical band gap. [ABSTRACT FROM AUTHOR]

A detailed study of the carrier absorption (CA) mechanism in multilayered silicon-nanocrystals (Si-nc) rib waveguides is reported. A pump (532 nm) and probe (1535 nm) technique is used to assess two loss mechanisms due to optical excitation of the system: one characterized by slow (seconds) dynamics related to heating and the other characterized by fast (microsecond) dynamics associated to CA mechanisms within the Si-nc. CA losses increase with pumping flux of up to 6 dB/cm for 3×1020 photons/cm2 s. By comparing the temporal dynamics of CA losses and time resolved photoluminescence, we suggest that both are determined by exciton generation and recombination. [ABSTRACT FROM AUTHOR]

The mechanism of photoluminescence (PL) from Si nanocrystals (Si-nc’s) in Er-doped silica is investigated by a double-pulse technique. It is shown that the decay time and the spectral intensity of PL emission from Si-nc’s do not change when Si-nc’s are reexcited by a delayed pulse in the presence of still excited Er ions. Results are compatible with a strong quenching of photoexcited Si-nc’s through trap states and/or Auger-like interaction between Si-nc’s and Er ions, both in the excited states, while PL emission originates from excitonic recombination in Si-nc’s that do not couple to Er3+. [ABSTRACT FROM AUTHOR]

Abstract: We report on the fabrication and characterization of an efficient and CMOS compatible Si-based light source. Silicon-rich silicon oxide (SRSO)/SiO2 superlattices-doped planar optical microcavities have been grown by reactive magnetron sputtering. The devices were studied using reflectance and photoluminescence measurements. The reflectivity of the resonator is above 99.9% and the quality factor is reaching a value of 100. Modification of silicon nanocrystals emission is clearly observed in the visible and reveals narrow, intense and highly directional emission properties. [Copyright &y& Elsevier]

A newly developed X-ray technique is used, which is able to quantitatively combine texture, structure, anisotropic crystallite shape and film thickness analyses of nanocrystalline silicon films. The films are grown by reactive magnetron sputtering in a plasma mixture of H2 and Ar onto amorphous SiO2 and single-crystal (100)-Si substrates. Whatever the used substrate, preferred orientations are observed with texture strengths around 2–3 times a random distribution, with a tendency to achieve lower strengths for films grown on SiO2 substrates. As a global trend, anisotropic shapes and textures are correlated with longest crystallite sizes along the 〈111〉 direction but absence of 〈111〉 oriented crystallites. Cell parameters are systematically observed larger than the value for bulk silicon, by approximately 0.005–0.015 A˚. [Copyright &y& Elsevier]

Abstract: The conditions governing the optimization of the coupling rate between the Si nanoclusters (Si-NCs) and the Er ions within a silicon oxide (SO) matrix, in terms of size, density and distribution of the Si-NCs and, more particularly, of the characteristic Er–carrier interaction distance, are investigated for single and multilayers (MLs) obtained by reactive magnetron sputtering. The maximum density of the sensitizers Si-NCs was grown in a Si-rich silicon oxide (SRSO) layer for 50% of hydrogen in the plasma upon annealing at about 900°C. The Er photoluminescence (PL), or the amount of optically active Er ions, was thus enhanced by about one order of magnitude with respect to the standard conditions. The impact of the size of Si-NC and of that of its separating distance from the neighboring Er ions on the efficiency of the energy transfer process were examined through studies performed on two configurations of MLs: SRSO:Er/SO (ML-A) and SRSO/SO:Er (ML-B). The comparison of the PL spectra obtained from both configurations shows that the Er emission at 1.54μm is a few tens of times higher for ML-A than for ML-B, because of the closer proximity between the Er ions and the Si-NCs formed within the former configuration. By varying the thickness of the SRSO:Er sublayer for the ML-A, which limits the size of the growing Si-NCs, the energy transfer process from Si-NC to Er becomes less efficient (and probably absent) when the size of Si nanograin reaches and exceeds 5nm. On the other hand, the increase of the SO:Er thickness for ML-B reveals that the Er PL increases and then saturates for an optimum value of the Er–NC spacing. The PL behavior has been reproduced by an exponentially decreasing Er–carrier interaction with a characteristic interaction distance found dependent on the nature of the sensitizers: about 0.4±0.1nm for amorphous Si-NC and near 2.6±0.4nm for Si nanocrystal. [Copyright &y& Elsevier]

Thin films of silicate glass containing Si excess and Er ions were fabricated by magnetron co-sputtering technique before being annealed at 450 °C to precipitate the Si excess in Si nanoclusters. The structural features were examined by infrared (IR) absorption spectroscopy, X-ray diffraction and transmission electron microscopy, while the emission properties were examined by photoluminescence (PL) spectroscopy. The evolution of the PL spectra obtained with both resonant (488 nm) and non resonant (476.5 nm) excitation lines, shows evidence of an important enhancement of the 1.54 μm signal when the Er ions coexist with Si nanoclusters (Si-nc), even though these latter appear non crystallized. Such results represent the first evidence of energy transfer from Si-nc to Er ions in silicate glass, and recall strikingly the similar process observed so far for the counterpart Si-rich SiO2:Er films. [Copyright &y& Elsevier]