Croissance épitaxiale des matériaux semi-conducteurs III-V et IV sur graphène pour des applications optoélectroniques

L’hétéroépitaxie conventionnelle permet la croissance épitaxiale de couches cristallines de haute qualité sur des substrats compatibles. Cependant, en raison des désaccords de maille/thermique, la formation de défauts cristallins tels que les dislocations dans les couches hétéroépitaxiales entrave fortement l’hétérointégration de divers semi-conducteurs et le développement de dispositifs de haute performance. Alternativement, l’épitaxie Van der Waals (VdWE), un nouveau paradigme de croissance épitaxiale permet la croissance des semiconducteurs cristallins sur des matériaux 2D sans les contraintes susmentionnées. Ce nouveau concept d’hétéroépitaxie mettant en œuvre de faibles interactions de type VdW est principalement dicté par les propriétés de la surface des matériaux 2D. Le graphène, combinant la flexibilité mécanique et la faible liaison de surface, s’est avéré être l’un des matériaux 2D les plus populaires pour la croissance épitaxiale VdW. Ce concept a suscité un grand intérêt dans la communauté scientifique, mais sa mise en œuvre est entravée par la compréhension incomplète et immature des processus gouvernant l’étape de nucléation. Ainsi, cette question reste ouverte, car aucune solution viable n’a encore été proposée et il n’y a pas de vision claire sur cette étape fondamentale de la croissance. En effet, la nucléation étant un processus éphémère est très difficile à observer en détail avec les techniques d’analyse conventionnelles post-croissance. En outre, les chercheurs n’ont pas pu fournir de preuves tangibles pour les nombreuses spéculations proposées sur la cinétique des premiers stades de la croissance des semi-conducteurs à 3D sur le graphène (2D). Ce défi a soulevé la question suivante : « Le graphène est-il le substrat ultime pour résoudre les défis fondamentaux de l’hétérointégration des matériaux ayant des désaccords de maille? ». Pour cette raison, les mécanismes gouvernant la nucléation des matériaux sur graphène font l’objet de débats depuis plus d’une décennie. Dans cette thèse, nous avons démontré pour la première fois l’épitaxie VdW de Ge sur monocouche suspendue de graphène (S-SLG) par observation directe à l’intérieur d’un microscope électronique en transmission (TEM). Pour ce faire, la synthèse de couches de graphène de haute qualité a été développée. Le graphène a été synthétisé sur le Ge (100) par CVD en utilisant une voie compatible avec l’intégration verticale avec les semi-conducteurs. Lors de cette étude, nous avons démontré que l’état de surface du substrat joue un rôle crucial dans la qualité du graphène déposé. Ainsi, un traitement de surface efficace, basé sur l’acide bromhydrique (HBr) a été mis au point. En effet, des couches de graphène de haute qualité avec un ratio ID/IG aussi faible que 0,2 ont été obtenues sur substrat de Ge (100). Pour mieux contrôler la nucléation qui est la phase centrale de la croissance cristalline, nous proposons de nouvelles perspectives à partir des observations en temps réel de la croissance in situ de Ge sur graphène en utilisant un TEM à haute résolution (HR). Nous avons étudié les mécanismes clés régissant la nucléation et la croissance du matériau 3D sur la surface du graphène. Alors que la faible énergie de surface du graphène rend difficile la nucléation de Ge sur la surface propre sans défaut, une stratégie en deux étapes a été proposée : Nucléation à basse température (220 °C) et recuit à des températures plus élevées afin d’améliorer la qualité cristalline des cristaux de Ge. À travers les images HRTEM, nous avons déterminé une taille critique de 0,7-1 nm2 permettant la nucléation de Ge sur SLG. Cette taille critique, qui n’a jamais été rapportée avant ce rapport, est cohérente avec celle prédite par la théorie classique de la nucléation. En outre, les données en temps réel ont révélé que, en raison de faibles interactions vdW, les germes Ge peuvent flotter librement à la surface du substrat de graphène, et leuriv coalescence est gouverné par un processus de murissement d’Ostwald extrême rapide. Notre observation majeure, cependant, a été l’implémentation des doubles hétérostructures de Ge/SLG/Ge (3D/2D/3D). Dans les conditions expérimentales employées, nous avons découvert une diffusion verticale (DV) des particules de Ge à travers le réseau hexagonal compact du graphène. Un tel phénomène intrigant ne peut être observé à l’aide des méthodes conventionnelles d’analyse ex situ, qui sont normalement réalisées après la croissance. Ces résultats ont mis en évidence le mécanisme de croissance des semi-conducteurs sur les monocouches de graphène et ont offert une nouvelle voie vers des dispositifs hybrides semiconducteurs/graphène à hautes performances. Finalement, dans l’ambition d’optimiser la croissance de matériaux III-V avec de bonnes propriétés pour la VdWE, une nouvelle approche d’épitaxie hybride a été mise au point et évaluée. Cette technique hybride d’épitaxie, utilisant à la fois des sources solides et gazeuses, est alternative aux techniques standards comme l’épitaxie par faisceaux moléculaires (MBE) et chimiques (CBE). Les résultats expérimentaux de la croissance d’AlInAs et de GaInAs sur substrats d’InP, ont démontré que cette nouvelle approche est efficace pour croitre des couches avec d’excellentes propriétés cristallines, optiques et à faible dopage résiduel.Abstract : Conventional heteroepitaxy allows epitaxial growth of highly crystalline layers onto compatible substrates. However, due to the lattice/thermal mismatch, the formation of crystalline defects such as dislocations in heteroepitaxial layers severely impede the heterointegration of various semiconductors with complementary properties and the development of high-performance devices. Alternatively, Van der Waals epitaxy (vdWE), a new paradigm of epitaxial growth can enable the growth of crystalline semiconductors on 2D materials without the aforementioned constraints. This new concept of heteroepitaxy, mediated by weak VdW interactions, is mainly dictated by the surface properties of emerging 2D materials, which also have many novel electrical, optical, thermal, and mechanical properties. Graphene, a 2D material that combines mechanical flexibility and weak surface bonding, is found to be one of the most popular for VdW epitaxial growth. This is currently the subject of intense research in the community, but tangible exploitation of such a compelling phenomenon is impeded by the immature and incomplete understanding of the nucleation and growth processes. Therefore, the question remains open as no viable solution was reached yet and there is no clear picture of the nucleation step. In fact, the nucleation process, which is a fleeting event is very difficult to observe in detail by using conventional ex situ analyses. Besides, researchers could not provide hard evidence for the several speculations involving the kinetics of threedimensional (3D) crystal growth over 2D graphene, at early stages of growth process. This challenge raised the following question: “Is graphene the ultimate substrate to solve fundamental challenges of heterointegration of mismatched materials?” For matters as such, governing mechanisms for nucleation on graphene has been debated for more than a decade now; however, despite the promises of VdW epitaxy, the lack of understanding of basic phenomena is still a major obstacle to the new applications. In this thesis, we demonstrated for the first time, in-situ TEM observation of VdWE of Ge on freestanding single layer graphene suspended graphene monolayers (S-SLG). To do this, the synthesis of high-quality graphene layers was developed. Using a compatible approach for the monolithic integration of 3D semiconductors on 2D materials, graphene was synthesized on germanium (Ge) (100) by CVD. In this study, we demonstrated that the physical and chemical surface state of the substrate play a crucial role in the quality of deposited graphene layers. Thus, an effective surface treatment, based on hydrobromic acid (HBr) has been developed. Highquality graphene layers with an ID/IG ratio as low as 0.2 were obtained on Ge (100). To better control the nucleation that is the central phase of crystalline growth, we offer new perspectives from real-time observations of Ge's in situ growth on graphene using a highresolution TEM. Through meticulous analysis of the collected video data, we investigated the key mechanisms governing the nucleation and the growth of sp3-bonded 3D material on the weakly interacting graphene surfaces. Whereas the low surface energy of the graphene layer prevented the nucleation of Ge over pristine and defect-free graphene, a two-step strategy consists of nucleating at low temperature (220 °C) and annealing at higher temperatures, resulted in growth of highly crystalline quality Ge. In view of the high-resolution TEM images, we determined a critical size of 0.7-1 nm2 enabling the nucleation of Ge on SLG. This critical size, which has never been reported prior to this report, is consistent with the one predicted by the classical nucleation theory. Moreover, the real-time data revealed that, due to weak VdW interactions, the Ge germs can freely float on the surface of graphene substrate,vi making the coarsening process of Ge layer to be dominated by a very fast Ostwald ripening process. Our major finding, however, was achieved by examining the 3D/2D/3D (2D/2D/2D) configuration of the Ge/graphene/Ge double heterostructures. Under the experimental conditions employed in our work, we recorded a vertical diffusion (VD) of Ge particles through the closely packed hexagonal ring of single layers of graphene. Such an intriguing and yet unexplored phenomenon cannot be obtained by means of the conventional ex situ analysis methods, which are normally carried out after the growth of material. These findings highlighted the growth mechanism of semiconductors on graphene monolayers and provided a new path to high-performance semiconductor/graphene hybrid devices. Finally, in the ambition to optimize the growth of III-V materials with good properties for VdWE, a new hybrid epitaxy approach has been proposed and evaluated. This hybrid epitaxy technique, using both solid and gaseous sources, is an alternative approach to standard techniques such as molecular beam epitaxy (MBE) and chemical beam epitaxy (CBE). Experimental results of the growth of AlInAs and GaInAs on InP substrates showed that this new approach is effective in growing layers with excellent crystalline, optical properties, and low residual doping

Hybrid MBE-CBE Growth and Characterization of Al 0.48 In 0.52 As on InP(100) for avalanche photodiode applications Motivation

International audienceIn this work, we demonstrate the epitaxial growth of high quality, low strain and low background doping of Al0.48In0.52As at 500°C on Fe-doped semi-insulating InP(100) substrate by using hybrid MBE-CBE technique. The precursors that were used are: solid aluminum, solid indium, TriMethylIndium (TMIn) and thermally cracked arsine. Using Nomarski, we observed smooth surfaces for the as grown layers. High-Resolution X-ray Diffraction (HR-XRD) in the vicinity of the (004) reflexion shows a lattice mismatch in the range -137 to 127ppm. The carrier density of undoped layers, obtained by Hall measurement at room temperature, is as low as 3E+15 cm-3 which is three orders of magnitude lower than the identical layers grown by organometallics sources. Photoluminescence (PL) for Al0.48In0.52As at low temperature (LT) shows a good optical quality. The quality and purity of the alloys grown here are compatible with high performance APD for optical communication

Hybrid MBE-CBE Growth and Characterization of undoped In 0,53 Ga 0,47 As on Fe-InP(001) for avalanche photodiodes (APDs)

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Wafer-scale detachable monocrystalline Germanium nanomembranes for the growth of III-V materials and substrate reuse

Germanium (Ge) is increasingly used as a substrate for high-performance optoelectronic, photovoltaic, and electronic devices. These devices are usually grown on thick and rigid Ge substrates manufactured by classical wafering techniques. Nanomembranes (NMs) provide an alternative to this approach while offering wafer-scale lateral dimensions, weight reduction, limitation of waste, and cost effectiveness. Herein, we introduce the Porous germanium Efficient Epitaxial LayEr Release (PEELER) process, which consists of the fabrication of wafer-scale detachable monocrystalline Ge NMs on porous Ge (PGe) and substrate reuse. We demonstrate monocrystalline Ge NMs with surface roughness below 1 nm on top of nanoengineered void layer enabling layer detachment. Furthermore, these Ge NMs exhibit compatibility with the growth of III-V materials. High-resolution transmission electron microscopy (HRTEM) characterization shows Ge NMs crystallinity and high-resolution X-ray diffraction (HRXRD) reciprocal space mapping endorses high-quality GaAs layers. Finally, we demonstrate the chemical reconditioning process of the Ge substrate, allowing its reuse, to produce multiple free-standing NMs from a single parent wafer. The PEELER process significantly reduces the consumption of Ge during the fabrication process which paves the way for a new generation of low-cost flexible optoelectronics devices.Comment: 17 pages and 6 figures along with 3 figures in supporting informatio

Unraveling the Heterointegration of 3D Semiconductors on Graphene by Anchor Point Nucleation

International audienceAbstract The heterointegration of graphene with semiconductor materials and the development of graphene‐based hybrid functional devices are heavily bound to the control of surface energy. Although remote epitaxy offers one of the most appealing techniques for implementing 3D/2D heterostructures, it is only suitable for polar materials and is hugely dependent on the graphene interface quality. Here, the growth of defect‐free single‐crystalline germanium (Ge) layers on a graphene‐coated Ge substrate is demonstrated by introducing a new approach named anchor point nucleation (APN). This powerful approach based on graphene surface engineering enables the growth of semiconductors on any type of substrate covered by graphene. Through plasma treatment, defects such as dangling bonds and nanoholes, which act as preferential nucleation sites, are introduced in the graphene layer. These experimental data unravel the nature of those defects, their role in nucleation, and the mechanisms governing this technique. Additionally, high‐resolution transmission microscopy combined with geometrical phase analysis established that the as‐grown layers are perfectly single‐crystalline, stress‐free, and oriented by the substrate underneath the engineered graphene layer. These findings provide new insights into graphene engineering by plasma and open up a universal pathway for the heterointegration of high‐quality 3D semiconductors on graphene for disruptive hybrid devices

CVD growth of high-quality graphene over Ge (100) by annihilation of thermal pits

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Thermally Induced Formation of Etch Pits on Ge Surfaces under Conditions of CVD Graphene Growth

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Hybrid MBE-CBE Growth and Characterization of Al 0.48 In 0.52 As on InP(100) for avalanche photodiode applications Motivation

International audienceIn this work, we demonstrate the epitaxial growth of high quality, low strain and low background doping of Al0.48In0.52As at 500°C on Fe-doped semi-insulating InP(100) substrate by using hybrid MBE-CBE technique. The precursors that were used are: solid aluminum, solid indium, TriMethylIndium (TMIn) and thermally cracked arsine. Using Nomarski, we observed smooth surfaces for the as grown layers. High-Resolution X-ray Diffraction (HR-XRD) in the vicinity of the (004) reflexion shows a lattice mismatch in the range -137 to 127ppm. The carrier density of undoped layers, obtained by Hall measurement at room temperature, is as low as 3E+15 cm-3 which is three orders of magnitude lower than the identical layers grown by organometallics sources. Photoluminescence (PL) for Al0.48In0.52As at low temperature (LT) shows a good optical quality. The quality and purity of the alloys grown here are compatible with high performance APD for optical communication

Ortho-Directed Palladium-Catalyzed Direct C–H Functionalization of 3-Picolinyl- and 3-(2-Cyanoethyl)pyrimidin-4(3H)-ones with Aryl Halides

International audienceThe ortho-directed palladium-catalyzed direct C-H arylation of N-picolinyl pyrimidin-4-one was achieved with various aryl halides. The methodology was extended towards C-H arylation of pyrimidin-4-ones incorporating methoxy group and aryl groups at C5 site. The 2cyanoethyl was also evaluated as ortho-directed group. The methodology gives access to innovative N-substituted 2-and 2,5-diarylated pyrimidin-4-ones. The standard 3-step deprotection sequence of picolinyl group was also studied

In‐Situ Transmission Electron Microscopy Observation of Germanium Growth on Freestanding Graphene: Unfolding Mechanism of 3D Crystal Growth During Van der Waals Epitaxy

International audienceBreakthroughs in cutting-edge research fields such as hetero-integration of materials and the development of quantum devices are heavily bound to the control of misfit strain during heteroepitaxy. While remote epitaxy offers one of the most intriguing avenues, demonstrations of functional hybrid heterostructures are hardly possible without a deep understanding of the nucleation and growth kinetics of 3D crystals on graphene and their mutual interactions. Here, the kinetics of such processes from real-time observations of germanium (Ge) growth on freestanding single layer graphene (SLG) using in-situ transmission electron microscopy are unraveled. This powerful technique provides a unique opportunity to observe new and yet unexplored phenomena, which are not accessible to the standard ex situ characterizations. Through direct observations, remote interactions are elucidated between Ge crystals through the graphene layer in double heterostructures of Ge/graphene/Ge. Notably, the data show real-time evidence of vertical Ge atoms diffusion through the graphene layer. This phenomenon is attributed to the remote interactions of Ge atoms through the graphene lattice, due to its interatomic interaction transparency. Additionally, key mechanisms governing nucleation and initial growth in graphene were systematically determined. These findings enlighten the growth mechanism of graphene and provide a new pathway for disruptive hybrid semiconductor-graphene devices