181 research outputs found
Epitaxy of SrTiO3 on Silicon: The Knitting Machine Strategy
Saint-Girons, Guillaume et al.SrTiO3 (STO) crystalline layers grown on Si open unique
perspectives for the monolithic integration of functional oxides in silicon-based
devices, but their fabrication by molecular beam epitaxy (MBE) is challenging due
to unwanted interfacial reactions. Here we show that the formation of single-crystal
STO layers on Si by MBE at the moderate growth temperature imposed by these
interface reactions results from the crystallization of a partially separated amorphous
mixture of SrO and TiO2 activated by an excess of Sr. We identify the atomic
pathway of this mechanism and show that it leads to an antiphase domain
morphology. On the basis of these results, we suggest and test alternative STO
growth strategies to avoid antiphase boundary formation and significantly improve
the STO structural quality. The understanding provided by these results offers
promising prospects to crystallize perovskite oxides on semiconductors at moderate
temperature and circumvent the issue of parasitic interface reactions.This work was partly supported by the European projects
SITOGA (STREP FP7, grant number 619456) and TIPS (ICT
H2020, grant number 107347) as well as by the French ANR
programs HIRIS and DIAMWAFEL.Peer reviewe
Systèmes épitaxiés faiblement liés (le cas Ge/SrTiO3)
Dans un contexte où les limites intrinsèques des matériaux classiques de l industrie CMOS sont en passe d être atteintes du fait de la forte miniaturisation des composants, le développement de la microélectronique requiert la définition de nouvelles solutions pour combiner sur un même substrat (le silicium) des matériaux différents aux propriétés physiques variées. Ceci devrait permettre d intégrer sur silicium des fonctionnalités nouvelles. Parmi les matériaux d intérêt, les oxydes fonctionnels de la famille des pérovskites offrent une large gamme de propriétés et attirent donc une attention particulière. D autre part, la recherche se porte aussi sur les semi-conducteurs de la classe III-V et le Ge pour leurs propriétés optiques ou de transport de charges. Cependant, la grande hétérogénéité chimique et cristallographique entre ces matériaux rend leur association sur silicium par voie épitaxiale particulièrement délicate. Dans ce contexte, ce travail de thèse consiste en une étude approfondie de l interface Ge sur SrTiO3et des mécanismes à l origine des modes d accommodation et de croissance du semi-conducteur sur le substrat pérovskite. Les échantillons, fabriqués par épitaxie par jets moléculaires, ont été étudiés par caractérisations in situ, au synchrotron, diffraction de rayons X en incidence rasante et spectroscopie de photoémission. Des images de microscopie électronique en transmission sont venues compléter cette étude. La combinaison de ces résultats a permis de comprendre et de décrire deux aspects spécifiques des systèmes III-V et Ge sur SrTiO3. Le mode de croissance Volmer-Weber et la compétition entre les orientations cristallines(001) et (111) du Ge sont décrits dans une première partie. La relation d épitaxie de Ge/SrTiO3est identifiée et l influence des énergies d adhésion et de surface libre du semi-conducteur sur sa croissance est élucidée. Dans une deuxième partie, le mode d accommodation du Ge est plus spécifiquement étudié. La mise en place d un réseau de dislocations d interface est observée expérimentalement et analysée à l aide d un modèle numérique. Ce travail de thèse a permis de discuter de l interface d un système épitaxié très hétérogène et il ouvre des perspectives intéressantes, liées aux spécificités de l accommodation aux interfaces semi-conducteurs/oxydes, pour l intégration monolithique de Ge et de III-V sur des substrats d oxydes/Si.With the recent developments of the microelectronic industry, the intrinsic limits of the classical CMOS materials are being reached because of the strong miniaturization. Thus, the microelectronic industry is waiting for new solutions for combining, on the same substrate (silicon), different materials with various physical properties in the framework of integrating new functionalities on silicon. Research is now focusing on perovskite oxides because of the very wide range of properties they are offering (electronic, magnetic, etc.), but also on III-V semiconductors for the development of integrated photonic devices and on Ge for its electronic transport properties. However, combining these materials is challenging due to their strong chemical and crystallographic heterogeneity. Thus, this thesis focuses on the Ge/SrTiO3 system. The accommodation mode and growth mechanism have been studied by in situ, synchrotron-based, characterization methods like grazing incidence X-ray scattering and X-ray photoemission spectroscopy. The samples were prepared by molecular beam epitaxy. Transmission electron microscopy images complemented the study. The combination of these results have allowed for highlighting two specificities of the III-V or Ge/SrTiO3epitaxial systems. In a first chapter, the Volmer-Weber growth mode and a competition between (001)and (111)-oriented Ge islands is described. Epitaxial relationship between Ge and SrTiO3, chemical bonds at the interface and influence of adhesion and surface energies on the growth mode are described. In a second part, the specific accommodation mode of the Ge/SrTiO3 interface is studied. The development of a misfit dislocation network during the growth is experimentally observed and analyzed on the basis of a numerical model of the interface. This work provides state of the art understanding of the interface of weakly bonded epitaxial systems and opens interesting perspectives, especially related to the accommodation mode of semiconductors/oxides interfaces, for the monolithic integration of III-V or Ge on oxides/Si substrates.LYON-Ecole Centrale (690812301) / SudocSudocFranceF
Buried dislocation networks designed to organize the growth of III-V semiconductor nanostructures
We first report a detailed transmission electron microscopy study of
dislocation networks (DNs) formed at shallowly buried interfaces obtained by
bonding two GaAs crystals between which we establish in a controlled manner a
twist and a tilt around a k110l direction. For large enough twists, the DN
consists of a twodimensional network of screw dislocations accommodating mainly
the twist and of a one-dimensional network of mixed dislocations accommodating
mainly the tilt. We show that in addition the mixed dislocations accommodate
part of the twist and we observe and explain slight unexpected disorientations
of the screw dislocations with respect to the k110l directions. By performing a
quantitative analysis of the whole DN, we propose a coherent interpretation of
these observations which also provides data inaccessible by direct experiments.
When the twist is small enough, one screw subnetwork vanishes. The surface
strain field induced by such DNs has been used to pilot the lateral ordering of
GaAs and InGaAs nanostructures during metal-organic vapor phase epitaxy. We
prove that the dimensions and orientations of the nanostructures are correlated
with those of the cells of the underlying DN and explain how the interface
dislocation structure governs the formation of the nanostructures
Poisson ratio and bulk lattice constant of (Sr 0.25 La 0.75 )CrO 3 from strained epitaxial thin films
International audienceAbout 30 nm thick (001)-oriented (Sr0.25La0.75)CrO3 (SLCO) epitaxial thin films were grown by solid-source oxide molecular beam epitaxy on four different single-crystalline cubic or pseudo-cubic (001)-oriented oxide substrates: LaAlO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, SrTiO3 and DyScO3, which result in lattice mismatch ranging from-2% to +1.7%. All the films are of high-quality, flat and strained by the substrates. By assessing the evolution of the out-of-plane lattice parameter as a function of the in-plane lattice parameter of the samples, we determine both the Poisson ratio (ν = 0.32) and the bulk lattice constant (ab = 3.876 Å) of SLCO. The Poisson ratio significantly differs from LaCrO3 (ν = 0.23) and the (SrxLa1-x)CrO3 solid solution appears to obey structural Vegard's law. Since SLCO is the only one p-type transparent conductive oxide of perovskite structure and has promising thermoelectric properties, integrating SLCO in heterostructures and devices is therefore of paramount importance, which confers on our results their strong interest. Besides, the method used here can be straightforwardly applied to other complex oxides
Electro-Optical Modulation Based on Pockels Effect in BaTiO3 With a Multi-Domain Structure
[EN] The influence of an in-plane multi-domain structure in BaTiO3 films grown on SrTiO3/Si buffers for highly efficient electro-optic modulation has been analyzed. The modulation performance can be significantly enhanced by rotating a certain angle, the optical waveguide, with respect to the BaTiO3 crystallographic axes. A robust electro-optical performance against variations in the domain structure as well as the lowest V-pi voltage can be achieved by using the rotation angles between 35 degrees and 55 degrees. Our calculations show that Vp voltages below 1.7 V for a modulation length of 2 mm can be obtained by means of a CMOS compatible hybrid silicon/BaTiO3 waveguide structure.This work was supported by the European Commission under Grant FP7-ICT-2013-11-619456 SITOGA. The work of P. Sanchis was supported in part by GVA under Grant PROMETEOII/2014/034 and in part by the Ministerio de Economia y Competitividad under Grant TEC2012-38540 LEOMIS.Castera, P.; Gutiérrez Campo, AM.; Tulli, D.; Cueff, S.; Orobtchouk, R.; Rojo Romeo, P.; Saint-Girons, G.... (2016). Electro-Optical Modulation Based on Pockels Effect in BaTiO3 With a Multi-Domain Structure. IEEE Photonics Technology Letters. 28(9):990-993. https://doi.org/10.1109/LPT.2016.252250999099328
Low-Loss and Compact Silicon Rib Waveguide Bends
[EN] Waveguide bends support intrinsically leaky propagation modes due to unavoidable radiation losses. It is known that the losses of deep-etched/strip waveguide bends increase inevitably for decreasing radius. Here, we theoretically and experimentally demonstrate that this result is not directly applicable to shallow-etched/rib waveguide bends. Indeed, we show that the total losses caused by the bends reach a local minimum value for a certain range of compact radii and rib waveguide dimensions. Specifically, we predicted the minimum intrinsic losses < 0.1 dB/90 degrees turn within the range of 25-30 mu m bend radii in a 220 nm-thick and 400 nm-wide silicon rib waveguide with 70 nm etching depth. This unexpected outcome, confirmed by experimental evidence, is due to the opposite evolution of radiation (bending) losses and losses caused by the coupling to lateral slab modes (slab leakage) as a function of the bend radius, hence creating an optimum loss region. This result may have important implications for the design of compact and low-loss silicon nanophotonic devices.This work was supported in part by the European STREP Program under Grant FP7-ICT-2013-11-619456-SITOGA and Grant FP7-ICT-2012-10-318240 PhoxTroT and in part by LEOMIS under Grant TEC2012-38540. (Corresponding author: Regis Orobtchouk.)Brimont, ACJ.; Hu, X.; Cueff, S.; Rojo-Romeo, P.; Saint Girons, G.; Griol Barres, A.; Zanzi, A.... (2016). Low-Loss and Compact Silicon Rib Waveguide Bends. IEEE Photonics Technology Letters. 28(3):299-302. https://doi.org/10.1109/LPT.2015.2495230S29930228
Integration of functional complex oxide nanomaterials on silicon
The combination of standard wafer-scale semiconductor processing with the properties of functional oxides opens up to innovative and more efficient devices with high value applications which can be produced at large scale. This review uncovers the main strategies that are successfully used to monolithically integrate functional complex oxide thin films and nanostructures on silicon: the chemical solution deposition approach (CSD) and the advanced physical vapor deposition techniques such as oxide molecular beam epitaxy (MBE). Special emphasis will be placed on complex oxide nanostructures epitaxially grown on silicon using the combination of CSD and MBE. Several examples will be presented, with a particular stress on the control of interfaces and crystallization mechanisms on epitaxial perovskite oxide thin films, nanostructured quartz thin films, and octahedral molecular sieve nanowires. This review enlightens on the potential of complex oxide nanostructures and the combination of both chemical and physical elaboration techniques for novel oxide-based integrated devicesAC acknowledges the financial support from 1D-RENOX project (Cellule Energie INSIS-CNRS). J.M.V.-F. also acknowledges MINECO for support with a Ph.D. grant of the FPI program. We thank David Montero and L. Picas for technical support. We also thank P. Regreny, C. Botella, J.B. Goure for technical assistance on the Nanolyon technological platform. We acknowledge MICINN (MAT2008-01022 MAT2011-28874-c02-01 and MAT2012-35324), Consolider NANOSELECT (CSD2007-00041), Generalitat de Catalunya (2009 SGR 770 and Xarmae), and EU (HIPERCHEM, NMP4-CT2005-516858) projects. The HAADF-STEM microscopy work was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. This research was supported by the European Research Council (ERC StG-2DTHERMS), Ministerio de Economía y Competitividad of Spain (MAT2013-44673-R) and EU funding Project “TIPS” Thermally Integrated Smart Photonics Systems Ref: 644453 call H2020-ICT-2014-1S
Giant tuning of electronic and thermoelectric properties by epitaxial strain in p-type Sr-doped LaCrO3 transparent thin films
The impact of epitaxial strain on the structural, electronic, and thermoelectric
properties of p-type transparent Sr-doped LaCrO3 thin films has been investigated. For this
purpose, high-quality fully-strained La0.75Sr0.25CrO3 (LSCO) epitaxial thin films were grown by
molecular beam epitaxy on three different (pseudo)cubic (001)-oriented perovskite-oxide
substrates: LaAlO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and DyScO3. The lattice mismatch between the
LSCO films and the substrates induces in-plane strain ranging from -2.06% (compressive) to
+1.75% (tensile). The electric conductivity can be controlled over two orders of magnitude, σ
ranging from ~0.5 S cm-1 (tensile strain) to 35 S cm-1 (compressive strain). Consistently, the
Seebeck coefficient S can be finely tuned by a factor of almost two from ~127 μV K-1 (compressive
strain) to 208 μV K-1 (tensile strain). Interestingly, we show that the thermoelectric power factor
(PF = S2 σ) can consequently be tuned by almost two orders of magnitude. The compressive strain
yields a remarkable enhancement by a factor of three for 2% compressive strain with respect to
almost relaxed films. These results demonstrate that epitaxial strain is a powerful lever to control
the electric properties of LSCO and enhance its thermoelectric properties, which is of high interest
for various devices and key applications such as thermal energy harvesters, coolers, transparent
conductors, photo-catalyzers and spintronic memories.Financial support from the European Commission through the
project TIPS (H2020-ICT-02-2014-1-644453), the French
national research agency (ANR) through the projects MITO
(ANR-17-CE05-0018), LILIT (ANR-16-CE24-0022), DIAMWAFEL (ANR-15-CE08-0034-02), the CNRS through the
MITI interdisciplinary programs (project NOTE), IDEX
Lyon-St-Etienne through the project IPPON, the Spanish
Ministerio de Ciencia e Innovación, through the “Severo
Ochoa” Programme for Centres of Excellence in R&D (SEV2015-0496) and the MAT2017-85232-R (AEI/FEDER, EU),
PID2019-107727RB-I00 (AEI/FEDER, EU), and from Generalitat de Catalunya (2017 SGR 1377) is acknowledged. The
China Scholarship Council (CSC) is acknowledged for the
grant of Dong Han. Ignasi Fina acknowledges Ramón y Cajal
contract RYC-2017-22531. Seebeck measurements at ILM
were made within the ILMTech transport platform. The
authors are also grateful to Jean-Baptiste Goure, Philippe
Regreny, Aziz Benamrouche, and Bernat Bozzo for their
technical support and the reviewers for their valuable and
constructive comments that have improved the quality of the
manuscript.Peer reviewe
Engineering the dielectric properties of functional oxides and integrating them on semiconductor platforms thanks to oxide molecular beam epitaxy
Séminaire invité donné à l’IME
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