Download or read book Free standing Epitaxial Graphene on Silicon Carbide and Transport Barriers in Layered Materials written by Shriram Shivaraman and published by . This book was released on 2013 with total page 157 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis is based on the topic of layered materials, in which different layers interact with each other via van der Waals forces. The majority of this thesis deals with epitaxial graphene (EG) obtained from silicon carbide (SiC). Free-standing epitaxial graphene (FSEG) structures are produced from EG using a photoelectrochemical (PEC) etching process developed for making suspended graphene structures on a large-scale. These structures are investigated for their mechanical and electrical properties. For doubly-clamped FSEG structures, a unique U-beam effect is observed which causes orders of magnitude increase in their mechanical resonance frequency compared to that expected using simple beam theory. Combined magnetotransport and Raman spectroscopy studies reveal that FSEG devices produced from nominally monolayer graphene on the Si-face of SiC exhibit properties of an inhomogeneously doped bilayer after becoming suspended. This suggests that the buffer layer which precedes graphene growth on the Si-face of SiC gets converted to a graphene layer after the PEC etching process. In the second theme of this thesis, transport barriers in layered materials are investigated. The EG-SiC interface is studied using a combination of electrical (I-V, C-V) and photocurrent spectroscopy techniques. It is shown that the interface may be described as having a Schottky barrier for electron transport with a Gaussian distribution of barrier heights. Another interface explored in this work is that between different layers of MoS2, a layered material belonging to the class of transition metal dichalcogenides. This interface maybe thought of as a one-dimensional junction. Fourpoint transport measurements indicate the presence of a barrier for electron transport at this interface. A simple model of the junction as a region with an increased threshold voltage and degraded mobility is suggested. The final chapter is a collection of works based on the topic of layered materials, which are not related to the main theme of the thesis. They include fabrication and characterization details of a dual-gated bilayer graphene device, an investigation of the graphene-Si interface and hexagonal boron nitride-based membranes. These are presented in the hope that they may be useful for further investigations along those directions.

Download or read book Epitaxial Graphene on Silicon Carbide written by Gemma Rius and published by CRC Press. This book was released on 2018-01-19 with total page 311 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is the first book dedicated exclusively to epitaxial graphene on silicon carbide (EG-SiC). It comprehensively addresses all fundamental aspects relevant for the study and technology development of EG materials and their applications, using quantum Hall effect studies and probe techniques such as scanning tunneling microscopy and atomic resolution imaging based on transmission electron microscopy. It presents the state of the art of the synthesis of EG-SiC and profusely explains it as a function of SiC substrate characteristics such as polytype, polarity, and wafer cut as well as the in situ and ex situ conditioning techniques, including H2 pre-deposition annealing and chemical mechanical polishing. It also describes growth studies, including the most popular characterization techniques, such as ultrahigh-vacuum, partial-pressure, or graphite-cap sublimation techniques, for high-quality controlled deposition. The book includes relevant examples on synthesis and characterization techniques as well as device fabrication processing and performance and complements them with theoretical modeling and simulation studies, which are helpful in the fundamental comprehension of EG-SiC substrates and their potential use in electronic applications. It addresses the fundamental aspects of EG-SiC using quantum Hall effect studies as well as probe techniques, such as scanning tunneling microscopy or atomic resolution imaging based on transmission electron microscopy. It comprises chapters that present reviews and vision on the current state of the art of experts in physics, electronic engineering, materials science, and nanotechnology from Europe and Asia.

Download or read book Free charge carrier properties in group III nitrides and graphene studied by THz to MIR ellipsometry and optical Hall effect written by Nerijus Armakavicius and published by Linköping University Electronic Press. This book was released on 2019-03-05 with total page 41 pages. Available in PDF, EPUB and Kindle. Book excerpt: Development of silicon based electronics have revolutionized our every day life during the last five decades. Nowadays silicon based devices operate close to their theoretical limits that is becoming a bottleneck for further progress. In particular, for the growing field of high frequency and high power electronics, silicon cannot offer the required properties. Development of materials capable of providing high current densities, carrier mobilities and high breakdown fields is crucial for further progress in state of the art electronics. Epitaxial graphene grown on semi-insulating silicon carbide substrates has a high potential to be integrated in current planar device technologies. High electron mobilities and sheet carrier densities make graphene extremely attractive for high frequency analog applications. One of the remaining challenges is the interaction of epitaxial graphene with the substrate. Typically, much lower free charge carrier mobilities, compared to free standing graphene, and doping, due to charge transfer from the substrate, is reported. Thus, a good understanding of the intrinsic free charge carriers properties and the factors affecting them is very important for further development of epitaxial graphene. Group III-nitrides have been extensively studied and already have proven their high efficiency as light emitting diodes for short wavelengths. High carrier mobilities and breakdown electric fields were demonstrated for group III-nitrides, making them attractive for high frequency and high power applications. Currently, In-rich InGaN alloys and AlGaN/GaN high electron mobility structures are of high interest for the research community due to open fundamental questions such as free charge carrier properties at high temperatures and wavefunction hybridization in AlGaN/GaN heterostructures. Electrical characterization techniques, commonly used for the determination of free charge carrier properties, require good ohmic and Schottky contacts, which in certain cases can be difficult to achieve. Access to electrical properties of buried conductive channels in multilayered structures requires modification of samples and good knowledge of the electrical properties of all electrical junctions within the structure. Moreover, the use of contacts to electrically characterize two-dimensional electronic materials, such as graphene, can alter their intrinsic properties. Furthermore, the determination of effective mass parameters commonly employs cyclotron resonance and Shubnikov-de Haas oscillations measurements, which require long scattering times of free charge carriers, high magnetic fields and low temperatures. The optical Hall effect is an external magnetic-field induced birefringence of conductive layers due to the free charge carriers interaction with long-wavelength electromagnetic waves under the influence of the Lorentz force. The optical Hall effect can be measured by generalized ellipsometry and provides a powerful method for the determination of free charge carrier properties in a non-destructive and contactless manner. The optical Hall effect measurements can provide quantitative information about free charge carrier type, concentration, mobility and effective mass parameters at temperatures ranging from few kelvins to room temperature and above. It further allows to differentiate the free charge carrier properties of individual layers in multilayer samples. The employment of a backside cavity for transparent samples can enhance the optical Hall effect and allows to access free charge carrier properties at relatively low magnetic fields using permanent magnet. The optical Hall effect measurements at mid-infrared spectral range can be used to probe quantum mechanical phenomena such as Landau levels in graphene. The magnetic field dependence of the inter-Landau level transition energies and optical polarization selection rules provide information about coupling properties between graphene layers and the electronic band structure. Measurement of the optical Hall effect by generalized ellipsometry is an indirect technique requiring subsequent data analysis. Parameterized optical models are fitted to match experimentally measured ellipsometric spectra by varying physically significant model parameters. Analysis of the generalized ellipsometry data at long wavelengths for samples containing free charge carriers by optical models based on the classical Drude formulation, augmented with an external magnetic field contribution, allows to extract carrier concentration, mobility and effective mass parameters. The development of the integrated FIR and THz frequency-domain ellipsometer at the Terahertz Materials Analysis Center in Linköping University was part of the graduate studies presented in this dissertation. The THz ellipsometer capabilities are demonstrated by determination of Si and sapphire optical constants, and free charge carrier properties of two-dimensional electron gas in GaN-based high electron mobility transistor structures. The THz ellipsometry is further shown to be capable of determining free charge carrier properties and following their changes upon variation of ambient conditions in atomically thin layers with an example of epitaxial graphene. A potential of the THz OHE with the cavity enhancement (THz-CE-OHE) for determination of the free charge carrier properties in atomically thin layers were demonstrated by the measurements of the carrier properties in monolayer and multilayer epitaxial graphene on Si-face 4H-SiC. The data analysis revealed p-type doping for monolayer graphene with a carrier density in the low 1012 cm-2 range and a carrier mobility of 1550 cm2V-1s-1. For the multilayer graphene, n-type doping with a carrier density in the low 1013 cm-2 range, a mobility of 470 cm2V-1s-1 and an effective mass of (0.14 ± 0.03)m0 were extracted. Different type of doping among monolayer and multilayer graphene is explained as a result of different hydrophobicity among samples. Further, we have employed THz-CE-OHE to determine for the first time anisotropic mobility parameter in quasi-free-standing bilayer epitaxial graphene induced by step-like surface morphology of 4H-SiC. Correlation of atomic force microscopy, Raman scattering spectroscopy, scanning probe Kelvin probe microscopy, low energy electron microscopy and diffraction analysis allows us to investigate the possible scattering mechanisms and suggests that anisotropic mobility is induced by varying local mobility parameter due to interaction between graphene and underlaying substrate. The origin of the layers decoupling in multilayer graphene on C-face 4H-SiC was studied by MIR-OHE, transmission electron microscopy and electron energy loss spectroscopy. The results revealed the decoupling of the layers induced by the increased interlayer spacing which is attributed to the Si atoms trapped between graphene layers. MIR ellipsometry and MIR-OHE measurements were employed to determine the electron effective mass in a wurtzite In0.33Ga0.67N epitaxial layer. The data analysis revealed the effective mass parameters parallel and perpendicular to the c-axis which can be considered as equal within sensitivity of our measurements. The determined effective mass is consistent with linear dependence on the In content. Analysis of the free charge carrier properties in AlGaN/GaN high electron mobility structures with modified interfaces showed that AlGaN/GaN interface structure has a significant effect on the mobility parameter. A sample with a sharp interface layers exhibits a record mobility of 2332 ± 73 cm2V-1s-1. The determined effective mass parameters showed an increase compared to the bulk GaN value, which is attributed to the penetration of the electron wavefunction into the AlGaN barrier layer. Temperature dependence of free charge carrier properties in GaN-based high electron mobility transistor structures with AlGaN and InAlN barrier layers were measured by terahertz optical Hall effect technique in a temperature range from 7.2 K to 398 K. The results revealed strong changes in the effective mass and mobility parameters. At temperatures below 57 K very high carrier mobility parameters above 20000 cm2V-1s-1 for AlGaN-barrier sample and much lower mobilities of ~ 5000 cm2V-1s-1 for InAlN-barrier sample were obtained. At low temperatures the effective mass parameters for both samples are very similar to bulk GaN value, while at temperatures above 131 K effective mass shows a strong increase with temperature. The effective masses of 0.344 m0 (@370 K) and 0.439 m0 (@398 K) were obtained for AlGaN- and InAlN-barrier samples, respectively. We discussed the possible origins of effective mass enhancement in high electron mobility transistor structures.

Download or read book Quantum Transport in Epitaxial Graphene on Silicon Carbide 0001 written by Johannes Jobst and published by . This book was released on 2013-02-28 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book 2 D Electronic Materials written by Dorr Oliver Campbell and published by . This book was released on 2015 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt: Graphene holds great promise as a material for high-speed electronics, especially as Si technology approaches its performance limits. Growth of epitaxial graphene by thermal decomposition of SiC is considered to be one of the most promising production routes since it has the potential to produce homogenous, wafer-size films directly on a semi-insulating or semiconducting substrate. Furthermore, graphene's planar 2-D structure enables devices and circuit designs with standard top-down lithography and processing techniques. However, the growth mechanism of graphene on SiC is not very well understood and much work remains to be done to improve the morphology, domain size and epitaxial quality of the grown graphene in order to take advantage of the unique properties of the material. This research work was aimed at using a modified CVD chamber in the Cornell University Wide-Bandgap-Semiconductor Laboratory to optimize the growth of epitaxial graphene by controlled decomposition of 6H-SiC(0001) in an argon mediated gas flow at near atmospheric pressure. Grown films were characterized using Raman spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and electrical measurements. Uniform large-area monolayer and few-layer epitaxial graphene were successfully grown on SiC terraces of up to 8 [MICRO SIGN]m wide, and with Hall mobilities of up to 840 cm2/V.s. The as-grown graphene was found to be intrinsically electron doped with sheet carrier density in the range of 3 - 9 x 1012 cm-2. However, certain growth features that tended to disrupt growth by uniform step flow decomposition were observed. These included deep rounded pits at higher temperatures, shallow triangular pits, arrow-like incursions across terraces, finger growths, residual SiC islands on terraces, nucleation of graphene at multiple defect points on terraces, and extra graphene layers at step edges. Further research is required to determine the mechanisms of formation of these features and to determine how they can be eliminated or reduced. For the first time SiC grown epitaxial graphene films, transferred from the substrate by a special process, was imaged in plan-view by TEM. The TEM images, along with selected-area electron diffraction, showed that a bilayer film had the AB Bernal stacking.!

Download or read book Integration of 2D Materials for Electronics Applications written by Filippo Giannazzo and published by MDPI. This book was released on 2019-02-13 with total page 265 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is a printed edition of the Special Issue "Integration of 2D Materials for Electronics Applications" that was published in Crystals

Download or read book Epitaxial Graphene on SiIicon Carbide written by Sang Won Lee and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The discovery of free-standing graphene in 2004 has attracted wide attention in both scientific community and industry because of its unusual electronic structure and properties. Due to the possible applications of graphene, many attempts to produce high-quality wafer-scale graphene films have been actively tried in the materials science and other scientific communities. Thermal decomposition of silicon carbide (SiC) is currently considered as one of the most promising routes toward the synthesis of well-controlled and characterized graphene films for electronic applications. This thesis focuses on the synthesis, structure and properties of epitaxial graphene on SiC. In the first chapter, I will investigate the structural properties of EG layers grown on the C-face of 4H-SiC in vacuum or Ar environments using synchrotron-based X-ray diffraction. The qualities and characteristics of layers will be also correlated with carrier mobilities obtained from Hall measurements. Since the Ar atmosphere produced higher quality graphene films on SiC than in vacuum, the inert-gas mediated thermal decomposition of SiC is regarded so far as the most effective method for the controlled EG growth. However, most studies have been done on the Si-face of SiC because of its slower reaction kinetics, which results in relatively uniform film thickness compared to the C-face. Nevertheless, there is significant interest in the C-face of SiC due to the superior electrical properties of EG grown on C-face SiC as compared to that grown on the Si-face. We find that Ar background pressure produces uniform graphene films on the C-face and the electronic properties (i.e. carrier mobility) of the films surpass that of vacuum-grown films due to larger crystalline domains formed in EG when the Ar pressure is above a certain threshold. In the second chapter, I will propose an alternative low-temperature, spatially controlled and scalable epitaxial graphene synthesis technique based on laser-induced surface decomposition of SiC. The high temperatures required in the conventional method are not compatible with large-scale device integration where different materials must be deposited and patterned prior to the formation of the semiconductor layer and limit the synthesis to single-crystal SiC substrates. Our technique is compatible with large-scale device integration. Furthermore, laser synthesis of graphene offers the advantage of combining synthesis and patterning in one step as the process can be designed to form graphene devices in predetermined locations on the substrate. In the last chapter, I will compare the structural properties of laser-synthesized EG on the Si-face and on the C-face of SiC. EG films on the C-face of 4H-SiC were successfully synthesized without the formation of carbon nanotubes by our laser technique, which are usually observed on the C-face upon vacuum high temperature anneals. The structural properties of these films were investigated by grazing incidence X-ray diffraction (GIXD) using synchrotron radiation and transmission electron microscopy. Since the graphene formation by UV laser irradiation is partially a photophysical process, I will illustrate the structural implications of the differences between the two formation processes.

Download or read book Properties of Synthetic Two Dimensional Materials and Heterostructures written by Yu-Chuan Lin and published by Springer. This book was released on 2018-10-23 with total page 141 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book represents a significant advance in our understanding of the synthesis and properties of two-dimensional (2D) materials. The author’s work breaks new ground in the understanding of a number of 2D crystals, including atomically thin transition metal dichalcogenides, graphene, and their heterostructures, that are technologically important to next-generation electronics. In addition to critical new results on the direct growth of 2D heterostructures, it also details growth mechanisms, surface science, and device applications of “epi-grade” 2D semiconductors, which are essential to low-power electronics, as well as for extending Moore’s law. Most importantly, it provides an effective alternative to mechanically exfoliate 2D layers for practical applications.

Download or read book Characterization of Selective Epitaxial Graphene Growth on Silicon Carbide written by Farhana Zaman and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The need for post-CMOS nanoelectronics has led to the investigation of innovative device structures and materials. Graphene, a zero bandgap semiconductor with ballistic transport properties, has great potential to extend diversification and miniaturization beyond the limits of CMOS. The goal of this work is to study the growth of graphene on SiC using the novel method of selective graphitization. The major contributions of this research are as follows - First, epitaxial graphene is successfully grown on selected regions of SiC not capped by AlN deposited by molecular beam epitaxy. This contribution enables the formation of electronic-grade graphene in desired patterns without having to etch the graphene or expose it to any detrimental contact with external chemicals. Etching of AlN opens up windows to the SiC in desirable patterns for subsequent graphitization without leaving etch-residues (determined by XPS). Second, the impact of process parameters on the growth of graphene is investigated. Temperature, time, and argon pressure are the primary growth-conditions altered. A temperature of 1400oC in 1 mbar argon for 20 min produced the most optimal graphene growth without significant damage to the AlN capping-layer. Third, first-ever electronic transport measurements are achieved on the selective epitaxial graphene. Hall mobility of about 1550 cm2/Vs has been obtained to date. Finally, the critical limitations of the selective epitaxial graphene growth are enumerated. The advent of enhanced processing techniques that will overcome these limitations will create a multitude of opportunities for applications for graphene grown in this manner. It is envisaged to be a viable approach to fabrication of radio-frequency field-effect transistors.

Download or read book Production and Properties of Epitaxial Graphene on the Carbon Terminated Face of Hexagonal Silicon Carbide written by Yike Hu and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Graphene is widely considered to be a promising candidate for a new generation of electronics, but there are many outstanding fundamental issues that need to be addressed before this promise can be realized. This thesis focuses on the production and properties of graphene grown epitaxially on the carbon terminated face (C-face) of hexagonal silicon carbide leading to the construction of a novel graphene transistor structure. C-face epitaxial graphene multilayers are unique due to their rotational stacking that causes the individual layers to be electronically decoupled from each other. Well-formed C-face epitaxial graphene single layers have exceptionally high mobilities (exceeding 10,000 cm 2/Vs), which are significantly greater than those of Si-face graphene monolayers. This thesis investigates the growth and properties of C-face single layer graphene. A field effect transistor based on single layer graphene was fabricated and characterized for the first time. Aluminum oxide or boron nitride was used for the gate dielectric. Additionally, an all graphene/SiC Schottky barrier transistor on the C-face of SiC composed of 2DEG in SiC/Si2O 3 interface and multilayer graphene contacts was demonstrated. A multiple growth scheme was adopted to achieve this unique structure.

Download or read book Charge Transport in Epitaxial Graphene on Silicon Carbide 0001 The Role of Mosaic like Disorder written by Ferdinand Kisslinger and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gateless Patterning in Epitaxial Graphene on Silicon Carbide 0001 Quantum Transport and THz Response written by Christian Sorger and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Application of Epitaxial Graphene Layers on Silicon Carbide in the Technology of Semiconductor Devices written by Tymoteusz Ciuk and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Growth and Magnetotransport Studies of Epitaxial Graphene written by Graham Leslie Creeth and published by . This book was released on 2010 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electrical Atomic Force Microscopy for Nanoelectronics written by Umberto Celano and published by Springer. This book was released on 2019-08-01 with total page 408 pages. Available in PDF, EPUB and Kindle. Book excerpt: The tremendous impact of electronic devices on our lives is the result of continuous improvements of the billions of nanoelectronic components inside integrated circuits (ICs). However, ultra-scaled semiconductor devices require nanometer control of the many parameters essential for their fabrication. Through the years, this created a strong alliance between microscopy techniques and IC manufacturing. This book reviews the latest progress in IC devices, with emphasis on the impact of electrical atomic force microscopy (AFM) techniques for their development. The operation principles of many techniques are introduced, and the associated metrology challenges described. Blending the expertise of industrial specialists and academic researchers, the chapters are dedicated to various AFM methods and their impact on the development of emerging nanoelectronic devices. The goal is to introduce the major electrical AFM methods, following the journey that has seen our lives changed by the advent of ubiquitous nanoelectronics devices, and has extended our capability to sense matter on a scale previously inaccessible.

Download or read book Silicon Carbide written by Wolfgang J. Choyke and published by Springer Science & Business Media. This book was released on 2013-04-17 with total page 911 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since the 1997 publication of "Silicon Carbide - A Review of Fundamental Questions and Applications to Current Device Technology" edited by Choyke, et al., there has been impressive progress in both the fundamental and developmental aspects of the SiC field. So there is a growing need to update the scientific community on the important events in research and development since then. The editors have again gathered an outstanding team of the world's leading SiC researchers and design engineers to write on the most recent developments in SiC.

Download or read book Lithium Batteries written by Gianfranco Pistoia and published by Elsevier Publishing Company. This book was released on 1994 with total page 502 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hardbound. Research in the area of lithium batteries has been quite eventful in the past few years. Some examples of recent achievements in the field are: the substitution of the Li anode with Li+-inserting carbonaceous materials, the discovery of polymer electrolytes with liquid-like conductivities at, or below, room temperature and the introduction of new oxide-based cathode materials with enhanced cyclability and energy density.This book aims at providing a factual and updated review of all new concepts which are emerging in research leading to the realization of commercial lithium batteries. An adequate balance of fundamental and applied research work is presented.A detailed description is given of systems ranging from thin-film, integrable batteries for microelectronics to high power, large batteries for industrial applications. Problem areas such as cost, safety and reliability are considered. The book will be of interest to materials