Yamina Andre

Local spin injectors using GaAs tips under light excitation

Local spin injectors using GaAs tips at the end of transparent cantilevers have been fabricated using a combination of epitaxial growth, etching processes and photolithographic techniques. The tip luminescence polarization is found to be small because of total internal light reflections of the luminescence inside the tip. However, measurements on planar films of similar doping along with a numerical solution of the spin and charge diffusion equations indicate that the injected spin polarization can be as high as 40% with corresponding electronic concentrations at the tip apex of the order of 1014u2002cm−3.

Hydride vapor phase epitaxy growth of III-V nanostructures for high performance devices

The fundamental performance limits of coherent optical transmission systems can be observed by a simple optimization between the linear noise and the nonlinear noise generated within the system. Optical Phase Conjugation (OPC) is considered to be one of the promising techniques to compensate for optical fiber’s dispersion and nonlinearity that cause crosstalk between signals traveling through long-haul optical transmission systems, nonlinearity compensation can lead to significant information capacity and distance reach expansion of optical fiber transmission links. To get the full benefit from the deployment of OPC in optical transmission systems, a few considerations must be taken into account, such as: power profile symmetry, fiber’s dispersion slope and Polarization Mode Dispersion (PMD). In this contribution, we will present our simplified theoretical predictions of optical fiber transmission systems performance that deploy mid-link OPC and multiOPC and we will show that the introduction of multi-OPC in an optical transmission system will minimize the impact of uncompensated/nondeterministic signal-signal nonlinear interactions due to fiber’s PMD and signal-noise interactions. We will show wide range of simulation and experimental results that validate the theoretical predictions of system’s performance for various types of links: dispersion managed, dispersion unmanaged, discretely amplified systems and distributed Raman amplified systems. Also, we will present an extensive experimental study shows that the deployment of mid-link OPC can provide a significant reach improvement in asymmetric lumped optical fiber links when optimizing the span length.III-V semiconductors have a direct bandgap that can be tuned through alloy engineering and therefore appear as very interesting for solar-cells, solid-state lighting and high power applications. The performances of current devices may be increased through the use of nanostructures and nanowires which look promising for the integration of high efficiency devices. Nanowires exhibit great properties such as efficient strain relieving capability and large specific area. Growth on silicon substrates and core-shell structures can be considered as well. Still, the production of nanowire-based devices faces material challenges related to morphological, structural, optical and electrical properties which are very linked to the synthesis process. nThis presentation will focus on Hydride Vapor Phase Epitaxy, which is a growth process implemented in a hot wall reactor using chloride precursors, and showing unique features regarding the growth of III-V and III-Nitride nanowires. For example, self-catalyzed GaAs nanowires were grown on silicon at a fast growth rate (60 µm.h-1) exhibiting a constant zinc-blende crystalline phase, for the potential fabrication of GaAs-based photonic devices on Si. For III-Nitride materials, InGaN nanowires demonstrating the entire composition range were grown by using a method compatible with the standard GaCl-based GaN growth process. Photoluminescence coupled with transmission electron microscopy measurements showed that these nanowires could overcome the so-called green gap and stretch the limits of solar cells efficiency. By taking advantage of the large growth rates anisotropy resulting from the use of chloride precursors, we could freely tuned the shape of GaN wires on masked substrates with (sub)-micrometric apertures.W the popularization of data centre and other bandwidth hungry inter-connect applications, the desired capacity of short reach optical network has exponentially increased to 400 Gbit/s or even more. Recent standardization efforts for 400 G intradata center connections specify link lengths of up to 2 km. 8×56 Gb/s or 4x100 Gb/s could enable such 400 G networks. Relative to coherent detection. Intensity modulation/direct detection (IM/DD) is a good candidate in inter-connect due to its low cost. For 56 and up to 100 Gb/s signal generation, a few modulation formats or schemes, such as pulse-amplitude-modulation (PAM4), discrete multitone (DMT), duobinary and chirp-managed laser (CML) are proposed and experimentally demonstrated. However, considering cost, size and power comsuption, the modulation format should be optimized for different networks to meet different requirements. In this talk, we will discuss this issue how to optimize the modulation formats for different optical networks?

Self-catalyzed growth of GaAs nanowires on silicon by HVPE

We report on the first self-catalyzed growth of GaAs nanowires on patterned and non-patterned silicon (111) wafers by hydride vapor phase epitaxy (HVPE) with a record elongation rate of 30 μm/h. The crystalline structure was analyzed using high resolution transmission electron microscopy (HRTEM). Self-catalyzed growth proceeds under gallium rich conditions at low-temperature (600 °C). Nanowires exhibit cylindrical rod-like shape morphology with a mean diameter of 50 nm and are randomly distributed.