N. Bertru

Institut National des Sciences Appliquées de Rennes | INSA Rennes · Département de Science et Génie des Matériaux (SGM)

Solar photoelectrochemical (PEC) H 2 production has the potential to solve one of the biggest issues confronting humanity nowadays: producing inexpensive, clean and renewable energy. Among various semiconductor materials, GaAs is an excellent candidate for the development of photoelectrodes within PEC cells for unassisted solar water splitting than...

The development of high-efficiency photoelectrodes at low manufacturing cost is of great interest for the production of renewable and green hydrogen through solar-driven water splitting. In this work, we use structural, optical, and photoelectrochemical characterizations to study the performance of unprotected epitaxial GaAs/Si photoelectrodes duri...

In this work, we demonstrate how the classical concept of band gap engineering usually used in III-V semiconductor devices can be extended to the engineering of the band lineup between...

Here, we comprehensively investigate the atomic structures and electronic properties of different antiphase boundaries in III-V semiconductors with different orientations and stoichiometries, including {110}, {100}, {111}, {112}, and {113}, based on first-principle calculations. Especially, we demonstrate how the ladder or zigzag chemical bond conf...

Here, we comprehensively investigate the atomic structures and electronic properties of different antiphase boundaries in III-V semiconductors with different orientations and stoichiometries, including {110}, {100}, {111}, {112} and {113} ones, based on first-principle calculations. Especially, we demonstrate how the ladder or zigzag chemical bond...

Hybrid materials taking advantage of the different physical properties of materials are highly attractive for numerous applications in today's science and technology. Here, it is demonstrated that epitaxial bi‐domain III–V/Si are hybrid structures, composed of bulk photo‐active semiconductors with 2D topological semi‐metallic vertical inclusions, e...

Highly polar materials are usually preferred over weakly polar ones to study strong electron-phonon interactions and its fascinating properties. Here, we report on the achievement of simultaneous confinement of charge carriers and phonons at the vicinity of a 2D vertical homovalent singularity (antiphase boundary, (APB)) in an (In, Ga)P/SiGe/Si sam...

Here we clarify the central role of the miscut during group III-V/group IV crystal growth. We show that the miscut impacts the initial antiphase domain distribution, with two distinct nucleation-driven (miscut typically >1°) and terraces-driven (miscut typically

Here, the structural, electronic and optical properties of the GaP1-xSbx/Si tandem materials association are determined in view of its use for solar water splitting applications. The GaPSb crystalline layer is grown on Si by Molecular Beam Epitaxy with different Sb contents. The bandgap value and bandgap type of GaPSb alloy are determined on the wh...

Here, we clarify the central role of the miscut during group III-V/ group IV crystal growth. We show that the miscut first impacts the initial antiphase domain distribution, with two distinct nucleation-driven and terraces-driven regimes. It is then inferred how the antiphase domain distribution mean phase and mean lateral length are affected by th...

The shape of InAs nanostructures formed by molecular beam epitaxy on a (001) InP substrate in the Stranski-Krastanow growth mode is studied. A transition from wires to round-shaped islands is observed as a function of the amount of InAs deposited. It is attributed to the non-equivalent energies of the A and B facets existing in zinc blende material...

Hydrogen production using artificial photosynthesis, i.e. solar splitting of water, is a promising energy alternative to fossil fuels. Efficient solar water splitting demands a suitable band gap to absorb near full spectrum solar energy and a photoelectrode that is stable in strongly alkaline or acidic electrolytes. In this work, we demonstrate for...

This work shows that a large‐scale textured GaP template monolithically integrated on Si can be developed by using surface energy engineering, for water‐splitting applications. The stability of (114)A facets is first shown, based on scanning tunneling microscopy images, transmission electron microscopy, and atomic force microscopy. These observatio...

Here, we experimentally and theoretically clarify III-V/Si crystal growth processes. Atomically-resolved microscopy shows that mono-domain 3D islands are observed at the early stages of AlSb, AlN and GaP epitaxy on Si, independently of misfit. It is also shown that complete III-V/Si wetting cannot be achieved in most III-V/Si systems. Surface/inter...

Taking advantage of low production costs and large integration scale, silicon photonics is a promising way to improve on-chip data routing and reduce electronic consumption. The small lattice mismatch between Si and GaP promotes the latter as a good candidate for III-V pseudomorphic integration, but questions remain on the interest of this platform...

In this work, we investigate the impact of growth parameters on surface morphology, doping levels and dopant activation in AlGaP epilayers grown on GaP substrate by solid source molecular beam epitaxy. Atomic Force Microscopy analysis reveals that a smooth surface can be obtained only in the [580-680]°C growth temperature range for a sufficiently l...

Here, we study the growth of n- and p-doped AlGaP alloys on GaP substrate, in view of their use in laser devices. The impact of growth temperature and growth rate on structural and electrical properties is studied with atomic force microscopy, C(V), Hall effect measurements, SIMS analysis and deep level transient spectroscopy (DLTS). Typical struct...

Room temperature electroluminescence of a GaP-based LED on Si and photoluminescence of (In,Ga)As quantum dots (QDs) located at 200nm of the III-V/Si interface were obtained, illustrating the good structural quality of the GaP/Si template used. The last step towards room temperature lasing on Si is thus reaching the direct bandgap emission. In this...

An atomic scale study has been performed to understand the influence of the (As,Sb) shutter sequences during interface formation on the optical properties of InGaAs/AlAsSb quantum wells. Our cross-sectional scanning tunneling microscopy results show that the onset of the Sb profile is steep in the Sb-containing layers whereas an appreciable segrega...

This study is carried out in the context of III–V semiconductor monolithic integration on silicon for optoelectronic device applications. X-ray diffraction is combined with atomic force microscopy and scanning transmission electron microscopy for structural characterization of GaP nanolayers grown on Si. GaP has been chosen as the interfacial layer...

Surfactant mediated growth of strained InAs/AlAs0.56 Sb 0.44 quantum wells on InP (001) substrate is investigated. X ray diffraction and transmission electron microscopy analysis reveal that the supply of antimony on InAs surface delays the 2D to 3D growth transition and allows the growth of thick InAs/AlAsSb quantum wells. Quantum well as thick as...

Epitaxie cohérente de composés GaP et GaAsPN à azote dilué sur substrats de Si pour l’élaboration de cellules PV tandem III-V/Si

GaAsPN semiconductors are promising material for the development of high-efficiency tandem solar cells on silicon substrates. GaAsPN diluted-nitride alloy is studied as the top-junction material due to its perfect lattice matching with the Si substrate and its ideal bandgap energy allowing a perfect current matching with the Si bottom cell. The GaP...

Annealing effect on electrical properties of GaAsPN solar cells

Thorough structural and optical analyses of GaP-based heterostructures monolithically grown on silicon substrates for photonics on Si applications: toward the laser on silicon and high efficiency photovoltaics on silicon

We report on Sb surfactant growth of InAs nanostructures on GaAs0.51Sb0.49 layers deposited on InP (001) and on (113)B oriented substrates. On the (001) orientation, the presence of Sb significantly favors the two-dimensional growth regime. Even after the deposition of 5 mono-layers of InAs, the epitaxial film remains flat and InAs/GaAs0.51Sb0.49 t...

Development of GaAsPN alloy for its integration in III-V/Si tandem solar cell

Impact of annealing on the performances of GaAsPN-based solar cells

The nature of the ground optical transition in (In, Ga)As/GaP quantum dots is thoroughly investigated through k·p calculations and a supercell tight-binding simulation. Quantum dot morphology is deduced from scanning-tunneling-microscopy images. The strain field has a strong influence on the conduction band states. Indeed, for a pure GaAs QD, the w...

Lattice-matched GaAsPN/GaP single junction solar cell for high-efficiency tandem solar cells on silicon

Optimisation des propriétés structurale de l’interface GaP/Si et des propriétés électroniques de cellules solaires GaAsPN/GaP pour la fabrication de cellule tandem

Analyse quantitative de la perfection cristalline de nanocouches épitaxiales GaP/Si

Abstract We report on the association of Ultra High Vaccum Chemical Vapor Deposition (UHVCVD) and Molecular Beam Epitaxy (MBE) to achieve III–V (GaP) integration on Si/Si(100) substrates. We first demonstrate that a very good flatness (0.3 nm) can be obtained when growing directly GaP on a chemically prepared Si substrate. X-ray diffraction pole fi...

We report on the quantitative study of microtwins (MT) defects in the GaP/Si(0 0 1) thin film grown by Molecular Beam Epitaxy and the optical properties of GaAsP(N)/GaP(N) quantum wells grown on top of the GaP/Si pseudo-substrates. A 780 nm photoluminescence at room temperature from the GaAsPN quantum wells is measured on silicon. Time-resolved pho...

In the context of III-V monolithic integration on silicon, synchrotron X-ray diffraction has been employed in this study using a bi-dimensional large area hybrid pixel detector (XPAD third generation) to characterize defects in the GaP layers. Despite a very coherent interface (low plastic relaxation) of GaP/Si, 2 types of defect are detected. Micr...

GaAsPN compounds for Si photonics

Intégration optique par croissance directe de nanostructures III-V sur silicium

The structural properties of (In,Ga)As/GaP quantum dots (QDs) are studied by plane view and cross scanning tunneling microscopy. Time-resolved and pressure dependent photoluminescence experiments show a ground optical transition of indirect type. Mixed k.p/tight-binding simulations indicate a possible indirect to direct crossover depending on indiu...

UHVCVD-MBE growth cluster for III-N-V/Si solar cells

We compare the potentiality of bulk InGaPN and GaAsPN materials quasi-lattice-matched to silicon (Si), for multi-junction solar cells application. Bandgaps of both bulk alloys are first studied by a tight-binding model modified for nitrogen incorporation in diluted regimes. The critical thicknesses of those alloys are then calculated for various co...

Enhanced incorporation of nitrogen on atomic step edges adsorption sites in diluted nitrides alloys

Lattice-matched GaP-based nanostructures grown on silicon substrates is a highly rewarded route for coherent integration of photonics and high-efficiency photovoltaic devices onto silicon substrates. We report on the structural and optical properties of selected MBE-grown nanostructures on both GaP substrates and GaP/Si pseudo-substrates. As a firs...

We have investigated the influence of the surface roughness on nitrogen incorporation during the molecular beam epitaxy of diluted nitrides, independently of the other growth parameters. GaPN/GaP layers grown simultaneously on surfaces displaying different roughnesses reveal a large difference in nitrogen incorporation despite the same growth tempe...

L’intégration d’émetteurs ou d’absorbeurs optiques efficaces sur substrat de silicium est un enjeu de taille pour d’une part le développement de la photonique sur silicium (lasers intégrés) et d’autre part les cellules solaires photovoltaïques très haut rendement. Dans cette communication, les derniers résultats sur la croissance cristalline direct...

(In,Ga)As/GaP(001) quantum dots (QDs) are grown by molecular beam epitaxy and studied both theoretically and experimentally. The electronic band structure is simulated using a combination of k.p and tight-binding models. These calculations predict an indirect to direct crossover with the In content and the size of the QDs. The optical properties ar...

We study in detail self-assembled (In,Ga)As quantum dots grown on GaP substrate from the structural, theoretical, and optical points of view. Single quantum dot morphology is first determined at the atomic level using plane-view scanning tunneling microscopy. Unusual C2 symmetry properties with high-index {136} facets are demonstrated for small qua...

We report a structural study of molecular beam epitaxy-grown lattice-matched GaP/Si(0 0 1) thin layers with an emphasis on the interfacial structural properties, and optical studies of GaAsP(N)/GaP(N) quantum wells coherently grown onto the GaP/Si pseudo substrates, through a complementary set of characterization tools. Room temperature photolumine...

We study the effect of Sb mediated growth on InAs layers on AlAsSb on InP substrate. The structural and optical characterisations show that InAs QW of at least 8ML can be grown without elastic relaxation in the presence of Sb on surface. Without Sb, critical thicknesses for Stranski-Krastanov transition thinner than 3ML are usually observed[6]. The...

The growth and thermalconductivity of InAsquantumdot (QD) stacks embedded in GaInAs matrix with AlAs compensating layers deposited on (1 1 3)B InP substrate are presented. The effect of the strain compensating AlAs layer is demonstrated through Atomic Force Microscopy (AFM) and X-ray diffraction structural analysis. The thermalconductivity (2.7 W/m...

Selected results obtained in the framework of MBE grown nanostructure for photonics on silicon are repsented in this paper. We present first a comprehensive study of GaAsPN/GaPN quantum wells (QWs) grown onto GaP substrates, in the light of a comparison with their N-free GaAsP/GaP QWs counterpart system. High density of small InGaAs/GaP Quantum Dot...

We have investigated quantitatively anti-phase domains (APD) structural properties in 20nm GaP/Si epilayers grown by molecular beam epitaxy, using fast, robust and non destructive analysis methods. These analyses, including atomic force microscopy and X-ray diffraction, are applied to samples grown by various molecular beam epitaxy growth modes. Ro...