arXiv subjects

Karim Ben Saddik

Publications and source records attributed to Karim Ben Saddik.

5 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 $μ$m, corresponding to oxide apertures of approximately 11-16 $μ$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↗

arXiv2024

Optomechanical cavities based on epitaxial GaP on nominally (001)-oriented Si

Gallium phosphide (GaP) has recently received considerable attention as a suitable material for building photonic integrated circuits due to its remarkable optical and piezoelectric properties. Usually, GaP is grown epitaxially on III-V substrates to keep its crystallinity and later transferred to silicon wafers for further processing. Here, an alternative promising route for the fabrication of optomechanical (OM) cavities on GaP epitaxially grown on nominally (001)-oriented Si is introduced by using a two-step process consisting of a low-temperature etching of GaP followed by selective etching of the underneath silicon. The low-temperature (-30 $^o$C) during the dry-etching of GaP hinders the lateral etching rate, preserving the pattern with a deviation between the design and the pattern in the GaP layer lower than 5 %, avoiding the complex process of transferring and bonding a GaP wafer to a silicon-on-insulator wafer. To demonstrate the quality and feasibility of the proposed fabrication route, suspended OM cavities are fabricated and experimentally characterized. The cavities show optical quality factors between 10$^3$ and 10$^4$, and localized mechanical resonances at frequencies around 3.1 GHz. Both optical and mechanical resonances are close to those previously reported on crystalline GaP structures. These results suggest a simple and low-cost way to build GaP-based photonic devices directly integrated on industry-standard Si(001) photonic wafers.

physics.optics↗

arXiv2021

A growth diagram for chemical beam epitaxy of GaP$_{1-x}$N$_{x}$ alloys on nominally $(001)$-oriented GaP-on-Si substrates

The dilute-nitride ternary compound GaP$_{1-x}$N$_{x}$ is highly attractive to monolithically integrate pseudomorphic red light-emitting devices and photovoltaic cells with the standard Si technology because it is lattice matched to Si with a direct band gap of $\approx1.96$ eV for $x=0.021$. Here, we report on the chemical beam epitaxy of GaP$_{x}$N$_{1-x}$ alloys on nominally $(001)$-oriented GaP-on-Si substrates. The incorporation of N into GaP$_{1-x}$N$_{x}$ was systematically investigated as a function of the growth temperature and the fluxes of the N and P precursors, 1,1-dimethylhydrazine (DMHy) and tertiarybutylphosphine (TBP), respectively. We found that the N mole fraction exhibits an Arrhenius behavior characterized by an apparent activation energy of $(0.79\pm 0.05)$ eV. With respect to the fluxes, we determined that the N mole fraction is linearly proportional to the flux of DMHy, and inversely proportional to the one of TBP. All results are summarized in an universal equation that describes the dependence of \textit{x} on the growth temperature and the fluxes of the group-V precursors. The results are further illustrated in a growth diagram that visualizes the variation of the chemical composition as the growth temperature and the flux of DMHy are varied. This diagram also shows how to obtain single-phase and flat GaP$_{1-x}$N$_{x}$ layers, as certain growth conditions result in chemically phase-separated GaP$_{1-x}$N$_{x}$ layers with rough surface morphologies. Last, our results demonstrate the feasibility of chemical beam epitaxy for the synthesis of single-phase and flat GaP$_{x}$N$_{1-x}$ layers with N mole fractions up to about $x=0.04$, a value well above the one required for the lattice-matched integration of GaP$_{1-x}$N$_{x}$-based devices on Si.

cond-mat.mtrl-sci↗