arXiv subjects

Alexandre Arnoult

Publications and source records attributed to Alexandre Arnoult.

7 recordsLinked to original sources

arXiv2026

Electrically-pumped near-infrared VCSEL epitaxially-grown on Si

The monolithic integration of compact laser sources onto silicon remains a critical bottleneck for the scalable development of silicon photonics. In particular, the direct epitaxial growth of near-infrared vertical-cavity surface-emitting lasers (VCSELs) on silicon has long been hindered by the simultaneous requirements of low crystalline defect density in the active region and smooth interfaces in the distributed Bragg reflector (DBR) mirrors, both essential to achieving high cavity quality factors and low lasing thresholds. Here, we report the direct epitaxial integration of near-infrared VCSELs on silicon substrates using a two-step growth strategy specifically designed to suppress defect propagation while preserving mirror interface abruptness. This approach enables effective confinement of threading dislocations away from the active region and ensures high-reflectivity DBRs with excellent structural uniformity. Structural and optical characterizations reveal an epitaxial stack of high crystalline quality, leading to laser performance comparable to VCSELs commonly grown on GaAs substrates. We demonstrate, for the first time, directly grown VCSELs on silicon wafers exhibiting threshold currents of only a few milliamperes. These results establish a decisive proof of concept for the monolithic integration of good-performance VCSELs onto silicon platforms and open a viable pathway toward fully integrated, low-cost silicon-based photonic systems.

physics.optics↗

arXiv2026

940-nm VCSELs grown by molecular beam epitaxy on Ge(001)

Vertical-cavity surface-emitting laser (VCSEL) structures emitting near 940 nm were grown by solid source molecular beam epitaxy (MBE) on Ge(001) substrates. The VCSEL MBE-growth was realized upon a virtual substrate composed of GaAs on Ge grown by melatorganic vapour phase epitaxy (MOVPE). In situ monitoring during MBE growth employed multispectral reflectometry and magnification-inferred curvature imaging for real-time growth analysis. Curvature measurements revealed progressive compressive stress, while optical reflectivity data confirmed uniform layer growth and accurate stopband formation. Fabricated devices with mesa diameters of 35-40 $\mu$m, corresponding to oxide apertures of approximately 11-16 $\mu$m, exhibited room-temperature lasing under continuous-wave bias with threshold currents below 3 mA. To the best of our knowledge, this is the first demonstration of monolithically integrated 940 nm VCSELs grown on Ge substrates by MBE. These results confirm the viability of MBE-grown VCSELs on Ge with in situ process control for scalable optoelectronic integration.

cond-mat.mtrl-sci↗

arXiv2025

Optical refractive index measurements of AlGaAs at high temperature for fully automated molecular beam epitaxy growth of Bragg mirrors

In-situ measurement is a key feature to better understand and precisely control the growth of complex structures, such as vertical-cavity surface-emitting lasers. In this work, we are showing the precise measurement of optical indices of AlGaAs at 600 {\textdegree}C over a wide spectral range (450--1400 nm). To do so, in-situ spectral reflectance measurement is used, combined with ex-situ layer thickness and composition measurement by x-ray diffraction enabling for precise determination of the optical indices with an accuracy better than 1%. To validate our measurements, we realized the complete automation of the growth of a GaAs/AlAs 940 nm-DBR by molecular beam epitaxy, without the need to pre-calibrate cells fluxes. The fabricated DBR shows a deviation of 0.2 nm of the stop-band central-wavelength compared to the targeted one. This approach holds significant interest for the III--V semiconductor community and epitaxial growth techniques.

cond-mat.mtrl-sci↗

arXiv2025

Data-driven Azimuthal RHEED construction for in-situ crystal growth characterization

Reflection High-Energy Electron Diffraction (RHEED) is a powerful tool to probe the surface reconstruction during MBE growth. However, raw RHEED patterns are difficult to interpret, especially when the wafer is rotating. A more accessible representation of the information is therefore the so-called Azimuthal RHEED (ARHEED), an angularly resolved plot of the electron diffraction pattern during a full wafer rotation. However, ARHEED requires precise information about the rotation angle as well as of the position of the specular spot of the electron beam. We present a Deep Learning technique to automatically construct the Azimuthal RHEED from bare RHEED images, requiring no further measurement equipment. We use two artificial neural networks: an image segmentation model to track the center of the specular spot and a regression model to determine the orientation of the crystal with respect to the incident electron beam of the RHEED system. Our technique enables accurate, and potentially real-time ARHEED construction on any growth chamber equipped with a RHEED system.

cond-mat.mes-hall↗

arXiv2024

Large-Scale Epitaxial Integration of Single-Crystalline BiSb Topological Insulator on GaAs (111)A

Topological insulators (TI) are promising materials for future spintronics applications and their epitaxial integration would allow the realization of new hybrid interfaces. As the first materials studied, Bismuth Antimony alloys (Bi1-xSbx) show great potential due to their tuneable electronic band structure and efficient charge-to-spin conversion. Here, we report the growth of Bi1-xSbx thin films on GaAs (111)A substrates following two different protocols. For the conventional epitaxy process, the grown films show excellent crystallinity and twin domains corresponding to an in-plane 180{\textdegree} rotation of the crystalline structure. Domain walls are found to be composition-dependent and have a lower density for Antimony-rich films. For the optimized process, depositing an Antimony bilayer prior to BiSb growth allows achieving single crystallinity of the TI films. The topologically protected surface states are evidenced by ex-situ ARPES measurements for domains-free and conventional films. To the best of our knowledge, this work presents the first large-scale epitaxial integration of single crystalline Bi1-xSbx thin films on industrial substrates.

cond-mat.mtrl-sci↗

arXiv2022

Monitoring MBE substrate deoxidation via RHEED image-sequence analysis by deep learning

Reflection high-energy electron diffraction (RHEED) is a powerful tool in molecular beam epitaxy (MBE), but RHEED images are often difficult to interpret, requiring experienced operators. We present an approach for automated surveillance of GaAs substrate deoxidation in MBE reactors using deep learning based RHEED image-sequence classification. Our approach consists of an non-supervised auto-encoder (AE) for feature extraction, combined with a supervised convolutional classifier network. We demonstrate that our lightweight network model can accurately identify the exact deoxidation moment. Furthermore we show that the approach is very robust and allows accurate deoxidation detection during months without requiring re-training. The main advantage of the approach is that it can be applied to raw RHEED images without requiring further information such as the rotation angle, temperature, etc.

cond-mat.mes-hall↗

arXiv2014

Investigation of the anisotropic electron g factor as a probe of the electronic structure of GaBi$_{x}$As$_{1-x}$/GaAs epilayers

The electron Land\'e g factor ($g^{*}$) is investigated both experimentally and theoretically in a series of GaBi$_{x}$As$_{1-x}$/GaAs strained epitaxial layers, for bismuth compositions up to $x = 3.8$%. We measure $g^{*}$ via time-resolved photoluminescence spectroscopy, which we use to analyze the spin quantum beats in the polarization of the photoluminescence in the presence of an externally applied magnetic field. The experimental measurements are compared directly to atomistic tight-binding calculations on large supercells, which allows us to explicitly account for alloy disorder effects. We demonstrate that the magnitude of $g^{*}$ increases strongly with increasing Bi composition $x$ and, based on the agreement between the theoretical calculations and experimental measurements, elucidate the underlying causes of the observed variation of $g^{*}$. By performing measurements in which the orientation of the applied magnetic field is changed, we further demonstrate that $g^{*}$ is strongly anisotropic. We quantify the observed variation of $g^{*}$ with $x$, and its anisotropy, in terms of a combination of epitaxial strain and Bi-induced hybridization of valence states due to alloy disorder, which strongly perturbs the electronic structure.

cond-mat.mtrl-sci↗