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The energy transfer process between amorphous silicon nanoparticles and erbium ions in Er-doped silicon-rich silicon oxide is investigated by fluorescence dynamics measurements. A fast decay is observed in the wavelength range of the radiative relaxation of erbium excited ions at 1.53 μm. Alternatively to a previous interpretation, we assign this fast decay to emission of deep traps induced by Si-based sensitizers of Er3+ ions, which emit in the visible and the infrared region. [ABSTRACT FROM AUTHOR]

Series of Er-doped Si-rich silicon oxide layers were studied with the aim of optimizing the coupling between Er ions and the Si-based sensitizers. The layers were grown at substrate temperature between 400 and 600 °C by the cosputtering of three confocal targets: Si, SiO2, and Er2O3. The influence of Si excess (5–15 at. %) and annealing temperature (500–1100 °C) was examined for two concentrations of Er ions (3.5×1020 and ∼1021 cm-3). We report the first observation of significant Er photoluminescence (PL) from as-grown samples excited by a nonresonant 476 nm line, with a lifetime in the range of 1.3–4 ms. This suggests the occurrence of an indirect excitation of Er through Si-based entities formed during the deposition. A notable improvement was observed for both Er PL intensity and lifetime after annealing at 600 °C. This temperature is lower than that required for phase separation, suggesting the formation of “atomic scale” sensitizers (Si agglomerates, for example) considered in recent work. For high Er doping (∼1021 cm-3), an optimum Er PL was obtained for the sample grown at 500 °C, annealed at 600 °C, and containing ∼13 at. % of Si excess. This high PL should correspond to an optimum fraction of coupled Er for this series, which was roughly estimated to about 11% of the total Er content for an excitation photon flux of few 1019 ph cm-2 s-1. For the moderately Er-doped series (3.5×1020 cm-3) grown at 500 °C, the optimum Er PL was found for the samples containing about 9 at. % silicon and annealed in the 600–900 °C range. The time decay reached a value as high as 9 ms for low Si excess (<6 at. %) and 6–7.5 ms for high values of Si excess. The fraction of Er ions coupled to sensitizers was similarly estimated for the best sample of this series and found to be as high as 22% of the total Er content. [ABSTRACT FROM AUTHOR]

The complex refractive index of SiO2 layers containing Si nanoclusters (Si-nc) has been measured by spectroscopic ellipsometry in the range from 1.5 to 5.0 eV. It has been correlated with the amount of Si excess accurately measured by x-ray photoelectron spectroscopy and the nanocluster size determined by energy-filtered transmission electron microscopy. The Si-nc embedded in SiO2 have been produced by a fourfold Si+ ion implantation, providing uniform Si excess aimed at a reliable ellipsometric modeling. The complex refractive index of the Si-nc phase has been calculated by the application of the Bruggeman effective-medium approximation to the composite media. The characteristic resonances of the refractive index and extinction coefficient of bulk Si vanish out in Si-nc. In agreement with theoretical simulations, a significant reduction of the refractive index of Si-nc is observed, in comparison with bulk and amorphous silicon. The knowledge of the optical properties of these composite layers is crucial for the realization of Si-based waveguides and light-emitting devices. [ABSTRACT FROM AUTHOR]

Resistive switching offers a promising route to universal electronic memory, potentially replacing current technologies that are approaching their fundamental limits. In many cases switching originates from the reversible formation and dissolution of nanometre-scale conductive filaments, which constrain the motion of electrons, leading to the quantisation of device conductance into multiples of the fundamental unit of conductance, G0. Such quantum effects appear when the constriction diameter approaches the Fermi wavelength of the electron in the medium - typically several nanometres. Here we find that the conductance of silicon-rich silica (SiOx) resistive switches is quantised in half-integer multiples of G0. In contrast to other resistive switching systems this quantisation is intrinsic to SiOx, and is not due to drift of metallic ions. Half-integer quantisation is explained in terms of the filament structure and formation mechanism, which allows us to distinguish between systems that exhibit integer and half-integer quantisation [ABSTRACT FROM AUTHOR]

The complex refractive index of SiO2 layers containing Si nanoclusters (Si-nc) has been measured by spectroscopic ellipsometry in the range from 1.5 to 5.0 eV. It has been correlated with the amount of Si excess accurately measured by x-ray photoelectron spectroscopy and the nanocluster size determined by energy-filtered transmission electron microscopy. The Si-nc embedded in SiO2 have been produced by a fourfold Si+ ion implantation, providing uniform Si excess aimed at a reliable ellipsometric modeling. The complex refractive index of the Si-nc phase has been calculated by the application of the Bruggeman effective-medium approximation to the composite media. The characteristic resonances of the refractive index and extinction coefficient of bulk Si vanish out in Si-nc. In agreement with theoretical simulations, a significant reduction of the refractive index of Si-nc is observed, in comparison with bulk and amorphous silicon. The knowledge of the optical properties of these composite layers is crucial for the realization of Si-based waveguides and light-emitting devices. [ABSTRACT FROM AUTHOR]

Abstract: This study compares the erbium emission from different Si-rich silicon oxynitrides matrices fabricated by magnetron sputtering. The Er-doped layers were grown by two different sputtering configurations: (i) standard co-sputtering of three confocal targets (Er2O3, Si3N4 and SiO2) under Ar plasma, and (ii) reactive co-sputtering under Ar+N2 plasma of either three (Er2O3, pure Si and SiO2) or two targets (Er2O3 and pure Si). The last reactive configuration was found to offer the best Er3+ PL intensity at 1.5μm. This highest PL intensity was found comparable to the corresponding emission from Er-doped silicon-rich silicon oxide. [Copyright &y& Elsevier]

Abstract: The structural and optical emission properties of Er-doped silicon-rich silica layers containing 1021 atcm−3 of erbium are studied as a function of deposition conditions and annealing treatment. Magnetron co-sputtering of three confocal targets (Si, SiO2 and Er2O3) under a plasma of pure argon was used to deposit the layers at 500°C. The silicon excess was varied in the layers in the range 7–15at% by monitoring the power applied on Si cathode. The as-grown samples were found significantly emitting at 1.54μm under non-resonant excitation. A maximum Er emission was observed after annealing at a moderate temperature (600°C) for any amount of Si excess, with a highest 1.54μm photoluminescence (PL) from the sample containing 13at% of Si. While no nanocrystals were observed in the samples annealed at 600°C, the sensitizers might, therefore, consist in ‘atomic’ scaled entities (Si agglomerates, for example) considered in recent similar work. The comparison of the emission features of our “best” sample and their counterparts reported so far, shows that the approach used this work allows to increase the fraction of the Er3+ ions coupled to Si sensitizers from 3% up to 12% of the total Er content. [Copyright &y& Elsevier]

Abstract: Er-doped silicon-rich silicon oxide layers have been grown at 600°C by magnetron co-sputtering of three confocal cathodes (Si, SiO2 and Er2O3) in pure argon plasma. The structural and optical properties of the layers were examined in the function of deposition and annealing conditions. It was shown that the increase of the RF power density applied on the Si cathode from 0.74 to 2.07Wcm−2, while maintaining constant RF power on the two other cathodes, allows a fine engineering of the Si excess from 5 to 15at%. The Er content was evaluated to 1×1021 atcm−3. A high Er3+ emission was observed under non-resonant (476nm) excitation from as-deposited layers, which was significantly improved after annealing at 600°C. The Er PL was found to be much more intense than the best samples reported so far, which was annealed at 900°C and contains, however, lower Er content (5.4×1020 atcm−3) and Si excess (7at% of Si). The Er emission lifetime was found to be about 6ms for low Si excess (5at%) and 1–2ms for high Si excess. Upon reducing the Er content by a factor of three, the Er3+ PL intensity was further increased and the lifetime reached 5.5ms, suggesting a notable increase of the fraction of coupled Er ions. [Copyright &y& Elsevier]

Abstract: The present article deals with the use of Si nanoclusters as efficient sensitizers towards Er3+ or Nd3+ ions. To take advantage from such an nc-mediated excitation, a maximum coupled rare-earth (RE) ions is sought through a careful engineering of the composition of the active material. For this purpose, confocal reactive magnetron co-sputtering process has been used for the fabrication of the co-doped layers. Depending on the deposition parameters and/or on annealing treatment, the photoluminescence (PL) properties of the RE ions have been analyzed and optimized. By an accurate monitoring of the deposition parameters and thermal treatment, the number of Er ions coupled to silicon nanocrystals has been multiplied by a factor of 4, with respect to the data reported so far for “standard” samples. Concerning neodymium, we have shown, on the other hand, that a concentration quenching occurs when the Nd concentration within the silicon-rich silicon oxide (SRSO) layer exceeds a threshold value, leading to a dramatic decrease of the Nd PL. Two decay times have been deduced from the time-resolved PL experiments and have been linked to the surrounding of the Nd3+ ions. [Copyright &y& Elsevier]

Abstract: Nd3+-doped silicon-rich silicon oxide (SRSO) single layers were grown by reactive magnetron sputtering silicon substrates. The photoluminescence (PL) properties were studied as a function of the Nd content. The PL intensity decreases due to the formation of Nd2O3 clusters when the Nd content is increased. The influence of both composition and temperature has been examined and the luminescence decays were fitted using two exponential law. At low temperature, the fast decay component, FDC (∼40μs) was attributed to Nd2O3 clusters and the slow component, SDC (∼240μs) was due to Nd-radiative transition. While the Nd concentration increase showed a detrimental effect on both components of the PL decays, the thermal activation of Nd3+ non-radiative de-excitation processes induced a significant decrease of the emission lifetime. [Copyright &y& Elsevier]