Évaluation du secteur communautaire du Service social de la Ville de Genève

Le Conseil administratif de la Ville de Genève a mandaté l'IDHEAP en tant qu'expert indépendant pour évaluer le secteur communautaire, une unité administrative rattachée au Service social. En prenant en considération les enjeux socio-sanitaires auxquels la Ville de Genève est confrontée, le concept d'étude proposé par l'Unité de politiques locales et d'évaluation de l'IDHEAP vise à établir un bilan de l'action du secteur communautaire, à déterminer la pertinence de cette action, son efficacité et son efficience, à tracer des perspectives en tenant compte notamment des prestations fournies par d'autres acteurs présents dans les domaines de la cohésion sociale et de la prévention socio-sanitaire, ainsi qu'à proposer des recommandations

Process Modules for GeSn Nanoelectronics with high Sn-contents

This paper systematically studies GeSn n-FETs, from individual process modules to a complete device. High-k gate stacks and NiGeSn metallic contacts for source and drain are characterized in independent experiments. To study both direct and indirect bandgap semiconductors, a range of 0 at.% to 14.5 at.% Sn-content GeSn alloys are investigated. Special emphasis is placed on capacitance-voltage (C-V) characteristics and Schottky-barrier optimization. GeSn n-FET devices are presented including temperature dependent I-V characteristics. Finally, as an important step towards implementing GeSn in tunnel-FETs, negative differential resistance in Ge0.87Sn0.13 tunnel-diodes is demonstrated at cryogenic temperatures. The present work provides a base for further optimization of GeSn FETs and novel tunnel FET devices

Optical Transitions in Direct-Bandgap Ge1-xSnx Alloys

A comprehensive study of optical transitions in direct-bandgap Ge0.875Sn0.125 group IV alloys via photoluminescence measurements as a function of temperature, compressive strain and excitation power is performed. The analysis of the integrated emission intensities reveals a strain-dependent indirect-to-direct bandgap transition, in good agreement with band structure calculations based on the 8-band k·p and deformation potential methods. We have observed and quantified Γ valley-heavy hole and Γ valley-light hole transitions at low pumping power and low temperatures in order to verify the splitting of the valence band due to strain. We will demonstrate that the intensity evolution of these transitions supports the conclusion about the fundamental direct bandgap in compressively strained GeSn alloys. The presented investigation, thus, demonstrates that direct-bandgap group IV alloys can be directly grown on Ge-buffered Si(001) substrates despite their residual compressive strain

Direct bandgap GeSn light emitting diodes for short-wave infrared applications grown on Si

The experimental demonstration of fundamental direct bandgap, group IV GeSn alloys has constituted an important step towards realization of the last missing ingredient for electronic-photonic integrated circuits, i.e. the e cient group IV laser source. In this contribution, we present electroluminescence studies of reduced-pressure CVD grown, direct bandgap GeSn light emitting diodes (LEDs) with Sn contents up to 11 at.%. Besides homojunction GeSn LEDs, complex heterojunction structures, such as GeSn/Ge multi quantum wells (MQWs) have been studied. Structural and compositional investigations con rm high crystalline quality, abrupt interfaces and tailored strain of the grown structures. While also being suitable for light absorption applications, all devices show light emission in a narrow short-wave infrared (SWIR) range. Temperature dependent electroluminescence (EL) clearly indicates a fundamentally direct bandgap in the 11 at.% Sn sample, with room temperature emission at around 0.55 eV (2.25 m). We have, however, identi ed some limitations of the GeSn/Ge MQW approach regarding emission e ciency, which can be overcome by introducing SiGeSn ternary alloys as quantum con nement barriers

GeSn lasers for CMOS integration

In search of a suitable CMOS compatible light source many routes and materials are under investigation. Si-based group IV (Si)GeSn alloys offer a tunable bandgap from indirect to direct, making them ideal candidates for on-chip photonics and nano-electronics. An overview of recent achievements in material growth and device developments will be given. Optically pumped waveguide and microdisk structures with different strain and various Sn concentrations provide direct evidence of gain in these alloys and the width of the emission wavelength range that can be covered. Towards the aim of electrically pumped lasers, a set of different homojunction light emitting diodes and more complex heterostructure SiGeSn/GeSn LEDs is presented. Detailed investigation of electroluminescence spectra indicate that GeSn/SiGeSn heterostructures will be advantageous for future laser fabrication

Transition to the quantum hall regime in InAs nanowire cross-junctions

We present a low-temperature electrical transport study on four-terminal ballistic InAs nanowire cross-junctions in magnetic fields aligned perpendicular to the cross-plane. Two-terminal longitudinal conductance measurements between opposing contact terminals reveal typical 1D conductance quantization at zero magnetic field. As the magnetic field is applied, the 1D bands evolve into hybrid magneto-electric sub-levels that eventually transform into Landau levels for the widest nanowire devices investigated (width = 100 nm). Hall measurements in a four-terminal configuration on these devices show plateaus in the transverse Hall resistance at high magnetic fields that scale with (ve 2 /h) -1 . e is the elementary charge, h denotes Planck's constant and v is an integer that coincides with the Landau level index determined from the longitudinal conductance measurements. While the 1D conductance quantization in zero magnetic field is fragile against disorder at the NW surface, the plateaus in the Hall resistance at high fields remain robust as expected for a topologically protected Quantum Hall phase. © 2019 IOP Publishing Ltd

Direct bandgap GeSn microdisk lasers at 2.5 μm for monolithic integration on Si-platform

We report on the first experimental demonstration of direct bandgap group IV GeSn microdisk (MD) lasers (λem=2.5 μm) grown on Si(001). The evidence of lasing is supported by a detailed analysis of strain-dependent emission characteristics of GeSn alloys with xSn ≥ 12 at.%. Residual compressive strain within the layer is relieved via under-etching of the MD enabling increased energy offsets up to EL-EΓ=80 meV. The lasing threshold and max. temperature amount to 220 kW/cm2 and 135 K, respectively

GeSn lasers for monolithic integration on Si

Lasing under optical pumping is shown in suspended GeSn microdisks fabricated on a Ge virtual substrate with a lasing threshold below 1 mW at 20K

Pyroglutamate Abeta pathology in APP/PS1KI mice, sporadic and familial Alzheimer’s disease cases

The presence of AβpE3 (N-terminal truncated Aβ starting with pyroglutamate) in Alzheimer’s disease (AD) has received considerable attention since the discovery that this peptide represents a dominant fraction of Aβ peptides in senile plaques of AD brains. This was later confirmed by other reports investigating AD and Down’s syndrome postmortem brain tissue. Importantly, AβpE3 has a higher aggregation propensity, and stability, and shows an increased toxicity compared to full-length Aβ. We have recently shown that intraneuronal accumulation of AβpE3 peptides induces a severe neuron loss and an associated neurological phenotype in the TBA2 mouse model for AD. Given the increasing interest in AβpE3, we have generated two novel monoclonal antibodies which were characterized as highly specific for AβpE3 peptides and herein used to analyze plaque deposition in APP/PS1KI mice, an AD model with severe neuron loss and learning deficits. This was compared with the plaque pattern present in brain tissue from sporadic and familial AD cases. Abundant plaques positive for AβpE3 were present in patients with sporadic AD and familial AD including those carrying mutations in APP (arctic and Swedish) and PS1. Interestingly, in APP/PS1KI mice we observed a continuous increase in AβpE3 plaque load with increasing age, while the density for Aβ1-x plaques declined with aging. We therefore assume that, in particular, the peptides starting with position 1 of Aβ are N-truncated as disease progresses, and that, AβpE3 positive plaques are resistant to age-dependent degradation likely due to their high stability and propensity to aggregate