Academic literature on the topic 'Cvd/mbe'

Strained isotopically enriched 28Si strained layers in SiGe/Si/SiGe heterostrustructures is an excellent material platform for electron spin qubits. In this work, we report the fabrication of 28SiGe/28Si/28SiGe heterostructures for qubit devices by a hybrid MBE/CVD growth, where the thick relaxed SiGe buffer is realized by a reduced-pressure CVD and the 28SiGe/28Si/28SiGe stack is grown by an MBE. Here, we achieve a fully strained 28Si layer in such heterostructure with a 29Si concentration as low as 200 ppm within the MBE grown layers. It was possible to conclude that 29Si primarily originates from the residual natural Si vapour in the MBE chamber. Furthermore, we also present our studies about the growth temperature effect on the misfit dislocation formation in this heterostructure. It was possible to show that at a low MBE growth temperature, such as 350°C, the misfit dislocation formation is significantly suppressed.

The structural properties of GeSn thin films with different Sn concentrations and thicknesses grown on Ge (001) by molecular beam epitaxy (MBE) and on Ge-buffered Si (001) wafers by chemical vapor deposition (CVD) were analyzed through high resolution X-ray diffraction and cross-sectional transmission electron microscopy. Two-dimensional reciprocal space maps around the asymmetric (224) reflection were collected by X-ray diffraction for both the whole structures and the GeSn epilayers. The broadenings of the features of the GeSn epilayers with different relaxations in the ω direction, along the ω-2θ direction and parallel to the surface were investigated. The dislocations were identified by transmission electron microscopy. Threading dislocations were found in MBE grown GeSn layers, but not in the CVD grown ones. The point defects and dislocations were two possible reasons for the poor optical properties in the GeSn alloys grown by MBE.

Molecular Beam Epitaxy (MBE) is a thin film deposition process in which thermal beams of atoms or molecules react on the clean surface of a single-crystalline substrate, held at high temperatures under ultrahigh vacuum conditions, to form an epitaxial film. Thus, contrary to the CVD processes described in the other articles, the MBE process is a physical method of thin film deposition.The vacuum requirements for the MBE process are typically better than 10−10torr. This makes it possible to grow epitaxial films with high purity and excellent crystal quality at relatively low substrate temperatures. Additionally, the ultrahigh vacuum environment allows the study of surface, interface, and bulk properties of the growing film in real time, by employing a variety of structural and analytical probes.Although the MBE deposition process was first proposed by Günther in 1958, its implementation had to wait for the development of the ultrahigh vacuum technology. In 1968 Davey and Pankey successfully grew epitaxial GaAs films by the MBE process. At the same time Arthur's work on the kinetics of GaAs growth laid the groundwork for the growth of high quality MBE films of GaAs and other III-V compounds by Arthur and LePore and Cho.

GeSn alloys have already attracted extensive attention due to their excellent properties and wide-ranging electronic and optoelectronic applications. Both theoretical and experimental results have shown that direct bandgap GeSn alloys are preferable for Si-based, high-efficiency light source applications. For the abovementioned purposes, molecular beam epitaxy (MBE), physical vapour deposition (PVD), and chemical vapor deposition (CVD) technologies have been extensively explored to grow high-quality GeSn alloys. However, CVD is the dominant growth method in the industry, and it is therefore more easily transferred. This review is focused on the recent progress in GeSn CVD growth (including ion implantation, in situ doping technology, and ohmic contacts), GeSn detectors, GeSn lasers, and GeSn transistors. These review results will provide huge advancements for the research and development of high-performance electronic and optoelectronic devices.

Two-dimensional layers of transition-metal dichalcogenides (TMDs) have been widely studied owing to their exciting potential for applications in advanced electronic and optoelectronic devices. Typically, monolayers of TMDs are produced either by mechanical exfoliation or chemical vapor deposition (CVD). While the former produces high-quality flakes with a size limited to a few micrometers, the latter gives large-area layers but with a nonuniform surface resulting from multiple defects and randomly oriented domains. The use of epitaxy growth can produce continuous, crystalline and uniform films with fewer defects. Here, we present a comprehensive study of the optical and structural properties of a single layer of MoS2 synthesized by molecular beam epitaxy (MBE) on a sapphire substrate. For optical characterization, we performed spectroscopic ellipsometry over a broad spectral range (from 250 to 1700 nm) under variable incident angles. The structural quality was assessed by optical microscopy, atomic force microscopy, scanning electron microscopy, and Raman spectroscopy through which we were able to confirm that our sample contains a single-atomic layer of MoS2 with a low number of defects. Raman and photoluminescence spectroscopies revealed that MBE-synthesized MoS2 layers exhibit a two-times higher quantum yield of photoluminescence along with lower photobleaching compared to CVD-grown MoS2, thus making it an attractive candidate for photonic applications.

The generation of semiconductor nanowires (NWs) by a “bottom-up” approach is of technological interest for the development of new nanodevices. In most cases Si and SiGe nanowires (NWs) are grown by molecular beam epitaxy (MBE) and by chemical vapor deposition (CVD) on the base of the vapor-liquid-solid-mechanism (VLS). In both cases small metal droplets act as a seed for the NW formation. The article mainly refers to the specific features of the MBE growth. The application of metals related to the VLS growth concept (quite often gold droplets are used) also causes several disadvantages of this approach, e.g., the formation of a metal wetting layer on all surfaces, dislocations, and electric active point defects. Concerning the formation of devices, technological steps, such as oxidation and doping of NWs, have to be considered. Specific techniques have to be applied to investigate the properties of individual semiconductor NWs. Some examples shall illustrate this topic.

Le graphène, une monocouche d'atomes de carbone hybridés sp2 dans un réseau hexagonal, fascine les scientifiques depuis les travaux pionniers des groupes d'André Geim et Walt de Heer en 2004. Les propriétés exceptionnelles du graphène, notamment sa mobilité électronique élevée et sa transparence optique, en font un matériau prometteur pour diverses applications en électronique et optoélectronique. Cette thèse vise la croissance du graphène sur germanium, un substrat qui pourrait être utilisé à la place du silicium pour les futurs dispositifs électroniques tels que les MOSFET, et qui présente par ailleurs l'avantage, contrairement au silicium, de ne pas former de liaisons fortes avec le carbone. Deux méthodes de croissances ont été étudiées : le dépôt chimique en phase vapeur (CVD), a priori plus adaptée à la production, et l'épitaxie par jets moléculaires (MBE) pour bénéficier des outils de suivi in-situ. Ce travail a commencé par une étude de la croissance du graphène par CVD sur le substrat de référence qu'est le carbure de silicium (SiC). Des travaux antérieurs ont déjà souligné les effets importants de l'hydrogène pendant la croissance du graphène, permettant de former à la fois une monocouche sur une couche tampon ou une multicouche sur une interface hydrogénée. Ici, nous avons également mis en évidence de forts effets de l'hydrogène pendant le refroidissement, puis développé un refroidissement sous argon permettant de les éviter. Cela nous a permis d'observer et d'étudier les étapes de la croissance du graphène sur une couche tampon et de mettre en évidence une autolimitation de la croissance à une monocouche, facilitant ainsi la croissance de films uniformes de graphène. Enfin, nous avons étudié comment le graphène se formait sur différents types de surfaces et de désorientation du SiC, mettant en évidence que l'uniformité et la reproductibilité étaient principalement limitées par les variations de désorientation résiduelle des substrats de SiC. Sur germanium, la CVD a également permis de faire croître des domaines de graphène de taille nanométrique, mais l'optimisation de la préparation de surface et de la croissance n'ont pas permis d'étendre la taille de ces domaines. Ce travail s'est ensuite focalisé sur la croissance de graphène sur germanium par MBE. Avant de faire croître le graphène, nous avons développé un nettoyage approprié de la surface du germanium dans la chambre MBE. Nous avons constaté que le chauffage du germanium à 600°C éliminait efficacement les oxydes et sous-oxydes indésirables de la surface. Cependant, pour garantir une surface atomiquement propre juste avant le dépôt de graphène, nous avons développé un processus de nettoyage en deux étapes basées sur un recuit initial de 30 minutes à 750°C, suivi d'un recuit flash de 5 minutes effectué à la température de croissance prévue. Nos recherches ont montré qu'en utilisant des températures de croissance d'environ 920°C, proches du point de fusion du germanium (937°C), nous avons pu produire du graphène. Les techniques de microscopie électronique à transmission (TEM) et de spectroscopie Raman ont été utilisées pour étudier la qualité du graphène obtenu. Bien que nous ayons réussi à faire croître du graphène, la détermination du nombre exact de couches de graphène s'est avérée difficile. Pour améliorer nos résultats, nous avons utilisé différents temps et températures de croissance, et constaté que des températures plus élevées produisaient généralement du graphène de meilleure qualité, même si nos meilleurs échantillons présentaient encore quelques défauts. Enfin, nous avons essayé de faire croître des hétérostructures potentiellement intéressantes pour des applications telles que le germanium sur du germanium recouvert de graphène, ce qui pourrait conduire à de nouvelles façons de fabriquer des dispositifs électroniques flexibles, ou du graphène sur SiGe, intéressant pour les applications en photodétection
Graphene, a single layer of sp2-bonded carbon atoms in a hexagonal lattice, has fascinated scientists since pioneering works by Andre Geim and Walt de Heer's groups in 2004. Graphene's exceptional properties, including high electron mobility and optical transparency, make it promising for various applications in electronics and optoelectronics.This thesis aims to grow graphene on germanium, a substrate that could be used instead of silicon for future electronic devices such as MOSFETs, and which also has the advantage, unlike silicon, of not forming strong bonds with carbon. Two growth methods were studied: chemical vapor deposition (CVD), which is a priori more suitable for production, and molecular beam epitaxy (MBE) to benefit from in-situ monitoring tools. This work began with a study of graphene growth by CVD on the reference substrate, silicon carbide (SiC). Previous work has already highlighted the significant effects of hydrogen during graphene growth, allowing the formation of both a monolayer on a buffer layer or a multilayer on a hydrogenated interface. Here, we have also demonstrated strong effects of hydrogen during cooling, and then developed cooling under argon to avoid them. This allowed us to observe and study the stages of graphene growth on a buffer layer and to demonstrate self-limitation of growth to a monolayer, thus facilitating the growth of uniform graphene films. Finally, we studied how graphene formed on different types of SiC surfaces and offcuts, showing that uniformity and reproducibility were mainly limited by variations in residual misorientation of SiC substrates. On germanium, CVD also allowed the growth of nanometer-sized graphene domains, but optimization of surface preparation and growth did not allow for extending the size of these domains.This work then focused on the growth of graphene on germanium by MBE. Before growing graphene, we developed an appropriate cleaning process for the germanium surface in the MBE chamber. We found that heating the germanium to 600°C effectively removed unwanted oxides and sub-oxides from the surface. However, to ensure an atomically clean surface immediately prior to graphene deposition, we developed a two-step cleaning process based on an initial 30-minute annealing at 750°C, followed by a 5-minute flash annealing conducted at the intended growth temperature. Our research showed that by using growth temperatures of approximately 920°C, which is near the melting point of germanium (937°C), we were able to produce graphene. Transmission Electron Microscopy (TEM) and Raman spectroscopy techniques were used to study the quality of the graphene obtained. While we were able to grow graphene successfully, determining the exact number of graphene layers proved challenging. To improve our results, we used different growth times and temperatures, and found that higher temperatures generally produced better quality graphene, even if our best samples still had some defects. Finally, we tried to grow heterostructures of potential interest for applications such as germanium on top of graphene-capped germanium, which could lead to new ways of making flexible electronic devices, or graphene on SiGe, interesting for photodetector applications

Dans le cadre de ce travail de thèse, nous avons étudié une approche permettant de réaliser les composants d'émission de la lumière basés sur les couches epitaxiées de Ge contraint en tension et fortement dopé de type n. Afin de créer de contrainte en tension dans les films épitaxiés de Ge, nous avons investi deux méthodes : faire croître du Ge sur InGaAs ayant un paramètre de maille plus grand que celui de Ge, et faire croître du Ge sur Si, en prenant l'avantage du coefficient de dilatation thermique du Ge, qui est deux fois plus grand que celui du Si. Concernant la croissance de Ge sur les substrats Si, nous avons étudié deux orientations cristallines, <001> and <111>, afin de pouvoir comparer la valeur de contrainte en tension obtenue et aussi la densité des dislocations émergeantes. Le dopage de type n dans le Ge a été effectué en utilisant le phosphore et l'antimoine. Nous avons montré que quand le dopage est effectué à des températures relativement basses et suivi d'un recuit thermique rapide, de concentration d'électrons électriquement activés de ~ 4x10^19 cm-3, a pu être obtenue. Cette valeur représente l'un des meilleurs résultats expérimentalement obtenus jusqu'à présent. Des mesures de recombinaison radiative par spectroscopie de photoluminescence effectuées à température ambiante ont mis en évidence une augmentation de l'émission du gap direct de Ge d'environ 150 fois. Finalement, nous avons étudié les effets de la barrière de diffusion sur l'efficacité de dopage pendant les recuits thermiques. Une comparaison sur l'efficacité de trois barrières de diffusion, Al2O3, HfO2 and Si3N4, sera présentée et discutée
During my thesis, we studied approaches to achieve light-emitting devices based on tensile strained and highly n-doped Ge epitaxial films. In order to create an elastic tensile strain in the epitaxial Ge films, we have investigated two methods: The epitaxial growth of Ge on InGaAs buffer layers that have a larger lattice constant, and the epitaxial growth of Ge on Si, by which we take benefit of the thermal expansion coefficient of Ge which is twice greater than that of Si. Concerning the growth of Ge on Si substrates, we have studied two crystalline orientations, <001> and <111>, in order to compare the values of the accumulated tensile strain and also the density of threading dislocations. The n-type doping in Ge was performed using a co-doping technique with phosphorus (P2 molecule) and antimony (Sb). We demonstrated that the dopants sticking coefficient leads to dopant incorporation in the Ge film larger than their solid solubility, which generally increases with increasing substrate temperature. As a result, when the doping is carried out at relatively low temperatures and followed by rapid thermal annealing, electrically activated electron concentration of 4x1019 cm-3 was demonstrated. This value is one of the best results obtained experimentally so far. The radiative recombination, at RT, measured by photoluminescence spectroscopy showed an increase in the direct gap emission of Ge of about 150 times. Finally, we studied the effects of diffusion barrier on the doping concentration during the thermal annealing. A comparison between the advantages of three diffusion barriers, Al2O3, HfO2 and Si3N4, will be presented and discussed

Le but de ce travail est la croissance du silicène sur Gr. J'ai décrit le substrat en fonction des conditions d’élaboration par CVD. Lorsque la proportion de H2 est faible il est possible d’obtenir du Gr homogène sur couche tampon (BL) sur SiC. Le STM et LEED montrent la superposition de la maille du Gr et de la reconstruction de la BL représentatif du Gr épitaxié. Lorsque la proportion de H2 est élevée la couche de Gr obtenue est totalement hydrogénée. Ceci est un résultat nouveau car aucun procédé d’intercalation d’hydrogène n’avait permis jusqu’à présent d’hydrogéner totalement les échantillons de (6x6)Gr épitaxié sur BL. Pour des proportions intermédiaires de H2/Ar, la coexistence de (6x6)Gr et H-Gr est observée. En fonction de la proportion de H2 dans le mélange gazeux, soit la surface du SiC reste passivée pendant toute la croissance du Gr et on obtient du H-Gr, soit le H2 désorbe partiellement, ou totalement et on obtient soit la coexistence des deux structures soit du (6x6)Gr pleine plaque. J’ai étudié la croissance par MBE de Si-ene sur (6x6)Gr. J’ai démontré qu'il est possible de former des flaques de Si-ene pour des épaisseurs de dépôt <0.5MC. Nous observons la présence de zones planes d’une épaisseur de 0.2-0.3nm correspondant à une monocouche de Si-ene, entourées d’îlots dendritiques 3D de Si. Les spectres Raman mettent en évidence un pic allant jusqu’à 563cm-1 ce qui est la valeur la plus proche du Si-ene FS jamais obtenue. Ces démontrent la formation de Si-ene quasi-FS. Ce travail contribue à une meilleure compréhension du mécanisme de croissance CVD du Gr et à l’avancement des recherches dans le domaine de la croissance épitaxiale des matériaux 2D
The topic of this thesis deals with the study of the growth and properties of silicene (Si-ene) on graphene (Gr) on 6H-SiC(0001) with the final goal of forming free-standing (FS) Si-ene on an insulating or semiconductor substrate. I have described the substrate as a function of the CVD processing conditions. When the proportion of H2 is low it is possible to obtain homogeneous Gr on buffer layer (BL) on SiC. The STM and LEED show the superposition of the Gr mesh and the BL reconstruction representative of the epitaxial Gr. When the proportion of H2 is high, the resulting Gr layer is fully hydrogenated. This is a new result as no hydrogen intercalation process has been able to fully hydrogenate (6x6)Gr samples epitaxial on BL until now. For intermediate proportions of H2/Ar, the coexistence of (6x6)Gr and H-Gr is observed. Depending on the proportion of H2 in the gas mixture, either the SiC surface remains passivated during the entire Gr growth and H-Gr is obtained, or the H2 partially or totally desorbs and either both structures coexist or full plate (6x6)Gr is obtained. I have studied the MBE growth of Si-ene on (6x6)Gr. I have shown that it is possible to form Si-ene puddles for deposit thicknesses <0.5MC. We observe the presence of flat areas of 0.2-0.3nm thickness corresponding to a Si-ene monolayer, surrounded by 3D dendritic islands of Si. The Raman spectra show a peak up to 563cm-1 which is the closest value to Si-ene FS ever obtained. This demonstrates the formation of quasi-FS Si-ene. This work contributes to a better understanding of the CVD growth mechanism of Gr and to the advancement of research in the field of epitaxial growth of 2D materials

L'évolution des technologies silicium atteint ses limites intrinsèques, entraînant un besoin d'innovations en matériaux et architectures pour la miniaturisation, la sensibilité et le faible consommation d'énergie dans les dispositifs électroniques.Les dichalcogénures de métaux de transition (TMDs), avec leur épaisseur atomique et leurs propriétés optoélectroniques uniques, suscitent un vif intérêt pour des applications telles que la photodétection et la détection de gaz. Cependant, la synthèse de TMDs de haute cristallinité, contrôlée par épitaxie par faisceau moléculaire (MBE), demeure un défi, limitant souvent les performances dans les applications pratiques. En parallèle, les nanotubes de carbone monoparoi (SWCNTs) offrent des propriétés uniques telles qu'une grande surface spécifique, une conductivité ajustable et une stabilité mécanique qui peuvent améliorer la fonctionnalité des dispositifs lorsqu'ils sont intégrés aux TMDs. La combinaison de ces matériaux dans une configuration hiérarchique ouvre des perspectives pour des dispositifs multifonctionnels performants. Cette thèse explore la synthèse et la caractérisation d'hétérostructures van der Waals (vdW) hybrides TMDs@SWCNTs de haute cristallinité et leur mise en œuvre dans des dispositifs. La croissance de TMDs (disulfure de molybdène (MoS₂) et disulfure de tungstène (WS₂)) par MBE a été investiguée. L'épitaxie par van der Waals de ces TMDs (MoS₂ et WS₂) a montré la capacité de former des structures de haute cristallinité sur de substrats à désaccord de maille (quartz et C-sapphire) sans compromettre l'intégrité du matériau. Nous avons exploré une approche novatrice basée sur des techniques ultra- vide (UHV), dans un réacteur construit maison, associant successivement le dépôt chimique en phase vapeur et à filament chaud (HF-CVD) avec la MBE, et permettant une croissance hautement contrôlée sur des substrats en quartz. Nous avons réussi à synthétiser des structures hybrides TMDs@SWCNTs qui exhibent une haute cristallinité, une épaisseur uniforme allant jusqu'à 10 nm, et un contact interfacial précis. Le rôle fondamental des SWCNTs dans le mécanisme de croissance de WS₂ et MoS₂ a été élucidé à travers des caractérisations poussées, in-situ/opérando et ex-situ, ce qui a permis de proposer un mécanisme de croissance basé sur les résultats expérimentaux obtenus. La caractérisation détaillée des matériaux, incluant la spectroscopie Raman, les techniques de spectroscopie électronique de surface et la microscopie électronique en transmission (TEM), met en évidence la croissance de haute cristallinité des couches de TMD sur les modèles de SWCNT, tout en prouvant le transfert de charge entre ces matériaux. En tant que canaux actifs, ces hétérostructures ont démontré d'excellentes propriétés optiques, atteignant une responsivité (~8,1 × 10³ A/W) et une détectivité (~2,91 × 10¹³ Jones) élevées pour la détection de la lumière proche de l'ultraviolet. De plus, la forte densité de sites exposés en bord de TMDs améliore l'adsorption des molécules de gaz et accélère la réponse dans les applications de détection. Des tests d'exposition à l'humidité ont montré la stabilité de ces hétérostructures, attribuée aux interactions électroniques à l'interface TMDs@SWCNTs. En outre, les hétérostructures présentent des propriétés électroniques intrinsèques contrastées et des effets de dopage ajustables (dopage P et N), soulignant leur polyvalence. Les travaux présentés ici mettent en évidence le potentiel des hétérostructures TMDs@SWCNTs en tant que matériaux innovants et performants pour les capteurs de gaz et les photodétecteurs de nouvelle génération. En approfondissant la compréhension des dynamiques de nucléation et de croissance des nanostructures hybrides, cette recherche ouvre la voie à l'intégration des TMDs et des SWCNTs dans des dispositifs de détection polyvalents en élargissant ainsi le champ des applications potentielles
The evolution of Si-based technologies is approaching intrinsic limits, driving the need for innovative materials and architectures that support advanced miniaturization, high sensitivity, and low-power operation in electronic devices. Among the promising candidates are transition metal dichalcogenides (TMDs), whose atomic-scale thickness and unique optoelectronic properties, have garnered attention for applications such as photodetection and gas sensing. However, achieving high-crystallinity TMDs synthesis, with controlled growth parameters, via molecular beam epitaxy (MBE), remains challenging, often limiting performance in practical applications. In parallel, single-walled carbon nanotubes (SWCNTs) offer unique properties, such as high specific surface area, tunable conductivity, and mechanical stability, that can enhance device functionality when integrated with TMDs. Combining the merit of these two classes of materials in a hierarchical arrangement can unlock a new realm of multifunctional devices with enhanced performance.This thesis explores the synthesis and characterization of high crystalline TMDs@SWCNTs van der Waals (vdW) hybrid heterostructures and their implementation in device structures.TMDs (molybdenum disulfide (MoS2) and tungsten disulfide (WS2) growth by MBE were investigated. The van der Waals epitaxial growth of these TMDs (MoS2 and WS2) has demonstrated high crystalline structures on large lattice-mismatched substrates (quartz and C-sapphire) without compromising material integrity. We explored a novel approach based on ultra-high vacuum techniques (UHV), in a home-built reactor, through sequential Hot-filament chemical vapor deposition (HF-CVD) /MBE offering highly controlled growth on quartz substrates. We achieved the synthesis of TMDs@SWCNTs hybrid structures that exhibit high crystallinity, uniform thickness up to 10 nm, and precise interfacial bonding. The fundamental role of SWCNTs in the growth mechanisms of WS2 and MoS2 is elucidated through comprehensive in-situ/operando and ex-situ characterizations, leading to a proposed growth mechanism based on the obtained experimental results.Detailed material characterization, including Raman spectroscopy, surface electron spectroscopy techniques, and transmission electron microscopy (TEM), demonstrates the structural integrity and high crystallinity of the TMD layers grown on SWCNT templates, while also confirming the charge transfer between these materials. Integrated as an active channel into a device, the as-grown heterostructures have proven remarkable optical properties, achieving high Responsivity (~8.1 × 103 A/W) and Detectivity (~2.91 × 1013 Jones) for detecting near-ultraviolet light. Additionally, the synthesized TMDs@SWCNTs exhibit a high density of exposed edge sites on TMD nanoflakes, that enhance the adsorption of target gas molecules and facilitate faster response in sensing applications. Environmental humidity exposure testing further demonstrated the stability of these heterostructures, which is attributed to the distinctive electronic interactions at the TMD-SWCNT interface. Moreover, the heterostructures display contrasting intrinsic electronic properties and tunable doping effects (p and n doping), underscoring their versatility and possibility to be integrated into multifunctional devices.The work presented here underscores the potential of TMDs@SWCNTs heterostructures as scalable, high-performance materials for next-generation gas sensors and photodetectors. By advancing the understanding of nucleation and growth dynamics of hybrid nanostructures, this research paves the way for integrating TMDs and SWCNTs into versatile sensing platforms with superior response characteristics, laying a foundation for applications spanning environmental monitoring and optoelectronics

abstract: Sn-based group IV materials such as Ge1-xSnx and Ge1-x-ySixSny alloys have great potential for developing Complementary Metal Oxide Semiconductor (CMOS) compatible devices on Si because of their tunable band structure and lattice constants by controlling Si and/or Sn contents. Growth of Ge1-xSnx binaries through Molecular Beam Epitaxy (MBE) started in the early 1980s, producing Ge1-xSnx epilayers with Sn concentrations varying from 0 to 100%. A Chemical Vapor Deposition (CVD) method was developed in the early 2000s for growing Ge1-xSnx alloys of device quality, by utilizing various chemical precursors. This method dominated the growth of Ge1-xSnx alloys rapidly because of the great crystal quality of Ge1-xSnx achieved. As the first practical ternary alloy completely based on group IV elements, Ge1-x-ySixSny decouples bandgap and lattice constant, becoming a prospective CMOS compatible alloy. At the same time, Ge1-x-ySixSny ternary system could serve as a thermally robust alternative to Ge1-ySny binaries given that it becomes a direct semiconductor at a Sn concentration of 6%-10%. Ge1-x-ySixSny growths by CVD is summarized in this thesis. With the Si/Sn ratio kept at ~3.7, the ternary alloy system is lattice matched to Ge, resulting a tunable direct bandgap of 0.8-1.2 eV. With Sn content higher than Si content, the ternary alloy system could have an indirect-to-direct transition, as observed for Ge1-xSnx binaries. This thesis summarizes the development of Ge1-xSnx and Ge1-x-ySixSny alloys through MBE and CVD in recent decades and introduces an innovative direct injection method for synthesizing Ge1-x-ySixSny ternary alloys with Sn contents varying from 5% to 12% and Si contents kept at 1%-2%. Grown directly on Si (100) substrates in a Gas-phase Molecular Epitaxy (GSME) reactor, both intrinsic and n-type doped Ge1-x-ySixSny with P with thicknesses of 250-760 nm have been achieved by deploying gas precursors Ge4H10, Si4H10, SnD4 and P(SiH3)3 at the unprecedented low growth temperatures of 190-220 °C. Compressive strain is reduced and crystallinity of the Ge1-x-ySixSny epilayer is improved after rapid thermal annealing (RTA) treatments. High Resolution X-ray Diffraction (HR-XRD), Rutherford Backscattering Spectrometry (RBS), cross-sectional Transmission Electron Microscope (XTEM) and Atomic Force Microscope (AFM) have been combined to characterize the structural properties of the Ge1-x-ySixSny samples, indicating good crystallinity and flat surfaces.
Dissertation/Thesis
Masters Thesis Chemistry 2019

The aim of this chapter is to develop an understanding of the electronic and optical properties of quantum well systems. These structures, which can be found in semiconductors, confine particles in one dimension and exhibit discrete energy levels that can be calculated using fundamental quantum mechanics. Quantum wells are formed by sandwiching a material like GaAs between two layers of a material with a wider bandgap like AlAs, and can be grown using techniques such as MBE or CVD. The electronic and optical properties of quantum wells can be modified by altering parameters such as potential and well widths. In this chapter, the authors will use the Schrödinger equation to solve for the energy levels of quantum wells and provide a quantum mechanical description of the properties of electrons in these systems. They will also use computer programs to investigate the effects of changing parameters such as potential and well widths on the properties of quantum wells.

Low-energy (≤ 200 eV) ion irradiation during crystal growth from the vapor phase can be used to provide new chemical reaction pathways, modify film-growth kinetics, and, hence, controllably alter the physical properties of films deposited by a variety of techniques. The latter includes sputter deposition, ion plating, plasma-assisted chemical vapor deposition (PA-CVD), primary-ion deposition (PID), and molecular-beam epitaxy (MBE) using accelerated beam sources. Ion/surface interaction effects such as ion-induced chemistry, trapping, recoil implantation, preferential sputtering, collisional mixing, enhanced diffusion, and alteration in segregation behavior are used to interpret and model experimental results concerning the effects of low-energy particle bombardment on nucleation and growth kinetics, elemental incorporation probabilities, compositional depth distributions, and the growth of metastable phases. Review articles on various aspects of ion irradiation during film growth including effects on nucleation and growth kinetics [1-4], microstructural evolution [4], preferred orientation and stress [2], elemental incorporation probabilities [1-3], dopant incorporation and depth distributions [5], and the synthesis of metastable semiconducting alloys [1-3,6] are available. Monte Carlo and molecular dynamics growth simulations have also been reviewed [4]. In this extended abstract, some of the key features of low-energy ion/surface interactions are outlined and new results are described.