Polarization strategies to improve the emission of Si-based light sources emitting at 1.55 μm

We present a electroluminescence (EL) study of the Si-rich silicon oxide (SRSO) LEDs with and without Er³⁺ ions under different polarization schemes: direct current (DC) and pulsed voltage (PV). The power efficiency of the devices and their main optical limitations are presented. We show that under PV polarization scheme, the devices achieve one order of magnitude superior performance in comparison with DC. Time-resolved measurements have shown that this enhancement is met only for active layers in which annealing temperature is high enough (>1000 °C) for silicon nanocrystal (Si-nc) formation. Modeling of the system with rate equations has been done and excitation cross-sections for both Si-nc and Er³⁺ ions have been extracted.     

Synthesis and spectral properties of Yb/Ho co-doped yttria 2 μm transparent ceramics

Yb/Ho co-doped yttria transparent ceramics, Yb/Ho:Y₂O₃, were prepared by vacuum sintering with additional 0.5 wt.% tetraethyl orthosilicate (TEOS) as sintering aid from the Yb/Ho co-doped yttria nanopowders synthesized by co-precipitation method. The optical quality of transparent ceramics was improved significantly, as increasing the sintering temperature from 1800 °C to 1850 °C as well as the holding time from 20 h to 25 h, respectively. The absorption spectrum was measured to find out the advisable emission source wavelength. The 2 μm emission bands were observed under laser diode excitation at 980 nm in the co-doped sample with 5 mol% of Yb³⁺ and 1 mol% of Ho³⁺, and broad emission bandwidth were obtained.     

Graphene-GaAs-graphene stacked layers for the improvement of the transmission at the wavelength of 1.55 μm

Transmission filter operating at the wavelength of 1.55 μm and based on stacked graphene-GaAs-graphene layers separated by air gaps is presented. By using the transfer matrix method (TMM), we show that the addition of a graphene layer at each interface of a GaAs-based stratified structure, which initially exhibit only 30% transmission at 1.55 μm, allows the active control of the transmission by the adjustment of the graphene chemical potential. Transmission of almost 100% at the wavelength of 1.55 μm is achieved after addition of graphene layers. These results show the potential role of stacked graphene-GaAs-graphene layers in the development of new optical active communications devices.     

Polarized spectroscopic properties of Ho-doped LuLiF4 single crystal for 2 μm and 2.9 μm lasers

Polarized spectroscopic properties of a Ho³⁺-doped LuLiF₄ (Ho:LuLF) single crystal grown by the Czochralski method have been investigated as a promising material for 2 μm and 2.9 μm lasers. The Judd-Ofelt (J-O) model has been applied to the analysis of the polarized room temperature absorption spectra to establish the so-called J-O intensity parameters. Based on the calculated parameters, we determined the emission probabilities, branching ratio and radiative lifetime for the Ho³⁺ transitions from the excited state manifolds to the lower-lying manifolds. Ho:LuLF crystal shows long fluorescence lifetime of ⁵I₇ manifold (16 ms) and broad absorption and emission spectra, which exhibit strong polarization characteristics. Stimulated emission cross-sections spectra of the ⁵I₆ → ⁵I₇ and ⁵I₇ → ⁵I₈ transitions were derived and compared with those of the other well-known Ho³⁺-doped laser crystals.     

Crystallization of amorphous silicon thin-film on glass substrate preheated at 650 °C using Xe arc flash of 400 μs

Experimental and theoretical investigations on flash lamp annealing (FLA) of amorphous silicon (a-Si) film on glass were carried out with a view to practical applications in large-window display industries. A Xe arc flash lamp of 950 mm in length and 22 mm in bore diameter was applied with nominal input voltage of 7 kV and flash duration of 400 μs. Prior to the annealing process, the specimen for FLA was preheated at 650 °C, which was very close to the service temperature of the glass specimen used in this study. By employing a focusing elliptic reflector, maximum light energy density of up to 8.4 J/cm² could be attained with an active exposure width of 2 cm. Crystallization of a-Si could be achieved in solid-phase by applying a flash beam with light density of at least 5 J/cm², and its phase-transition characteristics that varied with energy densities could be explained by theoretically estimated temperature fields. Electron microscopy observations confirmed that solid-phase crystallization preceded melting of a-Si due to relatively long flashing (heating) duration of 400 μs, which was comparable to solid-phase crystal-growth times at elevated temperatures.     

Er related 1.53 μm emission from Er-Si-codoped ZnO multilayer film prepared by rf-sputtering

The near-infrared emission from Er and Si codoped ZnO film, synthesized by cosputtering from separated Er, Si, and ZnO targets, has been investigated. By building the multilayer film structure, controlling the Er concentration, and optimizing the annealing condition, the intensity of Er³⁺ related 1.53 μm photoluminescence (PL), which originates from the transition of Er³⁺: ⁴I_13/2 → ⁴I_15/2, can be modulated. It is shown that the maximum intensities of Er³⁺ related 1.53 μm PL are obtained when the Si:ZnO/Er:Si:ZnO/Si:ZnO sandwiched multilayer film and the alternate Er:ZnO/Si:ZnO multilayer film were annealed at 1000 °C and 950 °C, respectively. The Er³⁺ related 1.54 μm PL intensity of the multilayer film is higher than that of the Er:ZnO monolayer film. This can be attributed to the presence of the silicon nanocrystals that could act as sensitizers of Er³⁺ ions in the multilayer film. The PL of the sandwiched multilayer film and the alternate multilayer film were measured under different temperatures (15-300 K). The sandwiched multilayer film exhibits a nonmonotonic temperature dependence as well as the alternate multilayer film, which differs from that of Er-doped ZnO as previously reported.     

Six image phase stepped photoelasticity for the quantification of the stress field around 25 μm reinforcing fibres

A six image phase stepped photoelastic technique has been applied for the measurement of the interfacial shear stress distribution in the matrix resin along a reinforcing E-glass fibre of ∼25 μm in diameter at its end and at a fibre-break. Contour maps of the isochromatic fringe order and its corresponding isoclinic angle, which are related to the principal stress difference and direction relative to the fibre axis, could be obtained continuously using this photoelastic technique. Thus the actual interfacial shear stress along the fibre can be calculated. Furthermore in the presence of a fibre-break, interfacial debonding and matrix yielding during stress transfer was investigated. The micro-mechanics are shown to differ at a fibre-break compared to a fibre-end.     

Efficient 1.53 μm emission and energy transfer in Si/Er-Si-O multilayer structure

Strong 1.53 μm light emission has been achieved in Si/Er-Si-O multilayer structure grown by sputtering method and annealing process. The luminescence intensity at 1.53 μm increases with annealing temperature, reaching maximum at about 800 °C, and decreases at higher temperatures. It is found that the amorphous Si well layer can sensitize and enhance Er³⁺ luminescence in Er-Si-O sublayer through carrier-mediated processes. Moreover, the Si/Er-Si-O multilayer exhibits much low temperature- and carrier-induced quenching of Er³⁺ luminescence, with the photoluminescence intensity at 1.53 μm decreased about a factor of only 1.4 from 80 K to 300 K. The new Si nanostructure material reported here may open the route towards the realization of electrically pumped Si-based light source.     

Effects of metal stacks and patterned metal profiles on the electromigration characteristics in super-thin AlCu interconnects for sub-0.13 μm technology

The electromigration (EM) characteristics of super-thin aluminum-copper alloy (AlCu) interconnects for sub-0.13 μm complementary metal-oxide-semiconductor logic technology were investigated by varying the AlCu underlayers and etched sidewall profile of AlCu wire. Super-thin AlCu wire with a Ti/TiN underlayer and a smooth etched sidewall profile was confirmed to have the best EM resistance in terms of the mean-time-to-failure (MTTF) and the failure distribution. The Ti/TiN underlayer is believed to lead to a longer MTTF by dramatically reducing the effective current density at the super-thin AlCu film in the entire of EM test line with a smaller formation of TiAl₃ at the TiN/AlCu interface. The smooth etched sidewall profile is considered to induce a steeper EM failure distribution by removing the early EM failure at the rough sidewall of aluminum. In terms of the location of EM-induced voids, the super-thin AlCu film inhibits the formation of EM-induced voids directly under the tungsten via by insignificant current crowding at the via-metal line corner.     

Study on the chemical stability of Y-doped BaCeO3 − δ and BaZrO3 − δ films deposited by aerosol deposition

Barium cerate (BaCeO₃) has high proton conductivity but rather poor chemical stability in CO₂-containing atmospheres. Barium zirconate (BaZrO₃), in contrast, is a rather stable material, but exhibits poor sinterability. In the present work, powders of Y-doped BaCeO₃ and BaZrO₃ were synthesized via the solid solution reaction method, and dense ceramic membranes with BaCe_0.9Y_0.1O₃ and BaZr_0.85Y_0.15O₃ were prepared by the aerosol deposition method at room temperature. Aerosol deposition method is a technique that enables the fabrication of ceramic films at room temperature with a high deposition rate as well as strong adhesion to the substrate. The powders and aerosol-deposited membranes were characterized by X-ray diffraction, particle size analysis, scanning electron microscopy, and X-ray elemental mapping. The chemical stability of powders and aerosol-deposited membranes with BaCe_0.9Y_0.1O₃ and BaZr_0.85Y_0.15O₃ against water and carbon dioxide has been investigated, and it was found that BaZr_0.85Y_0.15O₃ materials showed a better chemical compatibility.     

Single photon detection of degenerate photon pairs at 1.55 μm from a periodically poled lithium niobate parametric downconverter

Abstract

The performance of a communication system that uses 1.55 μm correlated photon pairs is analysed experimentally in terms of achievable coincidence rates, optimal pump rates, and the performance of custom-built photon-counting detectors at 1.55 μm. The testbed considered in this study uses standard telecom fibre, twin photons, and photon-counting detectors. Degenerate cw time-frequency entangled photon pairs are produced via quasiphase-matched spontaneous parametric downconversion in bulk periodically poled lithium niobate. The photon pairs are efficiently collected into a single-mode fibre and are sent to a pair of custom-built InGaAs photon-counting avalanche photodiodes that are passively quenched, gated in Geiger mode, and thermoelectrically cooled to temperatures as low as - 60°C. Reliable photoncounting operation with a quantum efficiency of 20% at a dark count probability of 0.04% per gate (20 ns) and negligible afterpulses is reported.     

Dy3+ doped GeGaSbS fluorescent fiber at 4.4 μm for optical gas sensing: Comparison of simulation and experiment

The infrared (IR) fluorescence from Dy³⁺ doped Ga₅Ge₂₀Sb₁₀S₆₅ fibers is investigated in details in order to develop bright IR fiber sources emitting at 4.4 μm for CO₂ sensing purposes. Optical sensing requires intense IR radiation to probe with accuracy gas concentrations by measuring the gas absorption. We developed a specific modeling describing the Dy³⁺ doped GeGaSbS fiber IR output power by simultaneously solving rate equations and propagation equations within the fibers. This modeling allows the determination of the IR fluorescence guided along the fiber as a function of the Dy³⁺ doping concentration, the propagation losses and the fiber geometry. The results of the simulation are successfully compared with experimental data and are further discussed in order to determine the optimal set of fiber characteristics maximizing the IR fiber output emission.     

Silicon-rich oxynitride hosts for 1.5 μm Er emission fabricated by reactive and standard RF magnetron sputtering

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 1.5 μm. This highest PL intensity was found comparable to the corresponding emission from Er-doped silicon-rich silicon oxide.     

Study of light absorption in n-type and p-type GaInAs and the possibility of making 1.55-μm GaInAs/InP Bragg mirrors

Effects of impurity doping on optical properties of epitaxially grown Ga_0.47In_0.53As semiconductors lattice-matched to InP have been studied. The absorption coefficient decreased and the photoluminescent peak energy increased at very high doping levels, due to a Burstein–Moss shift. Absorption in n-type Ga_0.47In_0.53As was negligible at a wavelength of 1.55 m when the donor (Si) concentration was higher than 7.7 × 10¹⁸cm^–3, but was higher than 4000 cm^–1 at = 1.3 m. Absorption in p-type Ga_0.47In_0.53As was 2600 cm^–1 and 7000 cm^–1 at 1.55 and 1.3 m, respectively, when the acceptor (Be) concentration was 3.4 × 10¹⁹cm^–3. Emission from n-type Ga_0.47In_0.53As experienced a maximum shift of 170 meV towards higher energies relative to emission from undoped Ga_0.47In_0.53As, while emission from p-type Ga_0.47In_0.53As shifted 45 meV. The Burstein–Moss effect was used in growth of 1.55-m distributed Bragg mirrors having 20 pairs of quarter-wave n–Ga_0.47In_0.53As/InP layers. Reflectivity greater than 95% and a stop-band width of 60 nm were demonstrated.     

Characterization of the mechanical properties changes in an Al–Zn–Mg alloy after a two-step ageing treatment at 70° and 135 °C

Fine-scale precipitation of the η′ phase and its precursors are essential for the mechanical properties of Al-4.6 wt%Zn-1.2 wt%Mg alloy. This paper deals with an investigation of precipitation in an industrial Al–Zn–Mg alloy at various stages of a conventional two-step ageing treatment at 70 °C and 135 °C. The effect of microstructure on the mechanical properties was performed using microhardness and tensile tests, together with optical, scanning and transmission electron microscopy. After ageing at 135 °C, corresponding to the maximum value of hardness, small η′ precipitates were observed in the alloy matrix. After two-step ageing at 70 °C plus at 135 °C, the volume fraction of this precipitate becomes higher. Consequently, the yield strength of the material increases and it maintains its ductility. This high precipitate density slows the dislocation movement and thus a higher stress was required for its bowing.     

Fast dynamics of 1.5 μm photoluminescence in Er-doped SiO2 sensitized with Si nanocrystals

In order to investigate origin of fast photoluminescence at 1.5 μm reported to appear in Er-doped SiO₂ sensitized with silicon nanocrystals, time-resolved photoluminescence measurements were compared between high temperature annealed Er-doped and Er-free samples. We confirm that this fast photoluminescence band observed in our materials is due to radiative recombination of Er³⁺ ions. At low temperatures, also a contribution from defect related-emission centered around 1300 nm appears and adds up to the Er-related emission.     

Direct observation of oxygen vacancy and its effect on the microstructure, electronic and transport properties of sputtered LaNiO3 − δ films on Si substrates

Highly (100)-oriented LaNiO₃ films with different oxygen content were deposited on Si substrates by radio frequency sputtering and post-annealed in oxygen and vacuum conditions. The formation of oxygen vacancies is directly observed by a decrease of lattice oxygen ratio in O 1s core-level photoelectron spectroscopy. X-ray diffraction measurement indicates that low oxygen pressure during the deposition or annealing process has a significant influence on the lattice constant of LaNiO₃ films. Further valence-band spectra and transport measurements demonstrate that the oxygen vacancies also have a significant influence on the electronic structure and transport behaviors of final LaNiO₃ films.     

Electrical characterisation of p-doped distributed Bragg reflectors in electrically pumped GaInNAs VCSOAs for 1.3 μm operation

The high resistivity that is encountered in p-type DBRs is an important problem in vertical cavity surface emitting lasers and optical amplifiers (VCSELs and VCSOAs). This is because the formation of potential barriers at the interfaces between layers of high and low refractive index inhibits the carrier flow, thus increasing the DBR series resistance. In this work, the electrical characteristics of two p-type doped DBR structures grown on undoped and p-type doped GaAs substrates have been investigated. The DBRs are designed for VCSOAs operating at 1.3 μm and consist of 14-periods of alternating GaAs and Al_0.9Ga_0.1As in the first sample and 14-periods of GaAs and Al_0.3Ga_0.7As/Al_0.9Ga_0.1As in the second one. For the longitudinal transport sample, Hall mobility and sheet carrier density were measured in the temperature range from 77 to 300 K. In the vertical transport sample, current–voltage (I–V) measurements across the DBR layers were carried out at different temperatures in the range between 15 and 300 K. We achieved resistivity reduction in our samples by using an interface composition grading technique aimed at improving the VCSOA characteristics.