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Vertical semiconductor nanowires have gained considerable attention in the last decade for their attractive optical and electronic properties. Their high surface to volume ratio and their ability to confine charge carriers and photons in one dimension has enabled them to be a promising candidate for improved as well as novel devices in nanophotonics and optoelectronics. However, it is necessary to achieve high quality nanowires with controllable features to fully understand and fine-tune the optical properties of the nanowires to achieve desired applications. In this study, various semiconductor materials like Gallium Arsenide (GaAs), Silicon and Amorphous Silicon (a-Si) were chosen to analyze and compare their optical properties using reflection measurements and finite difference time domain (FDTD) simulations. The nature of modal excitations in nanowires with the change in their diameter, pitch, shape and length are understood through simulation studies and verified using the measure- ments. Optical waveguiding, near field coupling, Fabry-Perot modes are comprehensively understood for the first time in the nanowire arrays. The ordered nanowires arrays are fabricated using Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) and a good understanding of the etching chemistries of chosen materials is achieved to fabricate high aspect ratio (length to diameter ratio) nanowire arrays. For GaAs nanowires, the aspect ratio of up to 73 is achieved with the controlled diameters for the very first time. For a variety of hard masks, etching parameters have been developed to get a good control over the sidewalls, diameters, and shapes of the nanowires. The silicon nanowires etching parameters are modified to achieve different shapes in lateral and longitudinal directions. Lastly, Gallium Nitride (GaN) nanowires are fabricated using chlorine chemistry with nitrogen as a clean passivation gas and wide varieties of masks and their combinations have been tested to achieve vertical morphology. iii Based on the understandings we achieved for the nanowires, a new platform is introduced for a-Si nanowires by etching them on a glass substrate and by integrating thin film with them to achieve the solar weighed absorptance 200-250 % higher than the thin film of the same thickness. Designs for broadband absorption in Gallium Arsenide nanowires are also considered and highest absorption achieved in those nanowires giving solar weighed absorption efficiency as high as 94%. This thesis spans both design of nanowire arrays for various applications, and fabrication and experimental verifications of them. As the comprehensive studies were done on the optical properties of the nanowire, the thesis presents a complete picture of various optical modes and phenomena, which emanate in them due to their interaction with light. It will provide optoelectronics engineers design directions as nanowire devices are considered in the future of commercial applications.
This book covers virtually all aspects of semiconductor nanowires, from growth to related applications, in detail. First, it addresses nanowires’ growth mechanism, one of the most important topics at the forefront of nanowire research. The focus then shifts to surface functionalization: nanowires have a high surface-to-volume ratio and thus are well-suited to surface modification, which effectively functionalizes them. The book also discusses the latest advances in the study of impurity doping, a crucial process in nanowires. In addition, considerable attention is paid to characterization techniques such as nanoscale and in situ methods, which are indispensable for understanding the novel properties of nanowires. Theoretical calculations are also essential to understanding nanowires’ characteristics, particularly those that derive directly from their special nature as one-dimensional nanoscale structures. In closing, the book considers future applications of nanowire structures in devices such as FETs and lasers.
Semiconductor Nanowires: Part A, Number 93 in the Semiconductor and Semimetals series, focuses on semiconductor nanowires. Contains comments from leading contributors in the field semiconductor nanowires Provides reviews of the most important recent literature Presents a broad view, including an examination of semiconductor nanowires Comprises up to date advancements in the technological development of nanowire devices and systems, and is comprehensive enough to be used as a reference book on nanowires as well as a graduate student text book
Vertically oriented nanowires are gaining a considerable amount of attention for a wide variety of applications ranging from lasers to solar cells. Raman spectroscopy has also been developed into a powerful tool which has been used to effectively measure the physical properties of nanowires including crystalline quality, and thermal properties. However, Raman spectroscopy has not widely been applied to study vertically oriented nanowires. In this thesis, it is shown that Raman spectra from vertically oriented nanowires can be used to understand the crystalline quality of the samples, and can also be used to identify the diameter for which the HE11 mode is resonantly excited for an incident wavelength of light. In addition to this, Raman spectroscopy was used to estimate the refractive index of the amorphous silicon nanowire samples. Secondly, enhanced photo-thermal conversion in vertically oriented nanowires is demonstrated. The temperatures are measured using Raman spectroscopy. It is shown that by exciting the HE11 mode that temperature increases of 300 K can be achieved for an irradiance of only 10 W/mm2. Furthermore it is shown that when higher irradiances are used, that GaAs nanowires begin to decompose, resulting in a shell morphology. The concept of photo-thermal heating due to waveguiding was also used to examine how the crystallization process of a-Si nanowires is affected. It was found that depending on the diameter of the nanowire, the crystallization is process is limited. Initial excitation of the HE11 mode does not lead to total crystallization due to a rapid loss in the resonance condition. Lastly, structural colours were observed from nanowire arrays. The colours are used to demonstrate a diffraction based method for measuring nanowire spacing, a linear refractive index sensor, and photo-thermal printing.
Semiconductor nanowires promise to provide the building blocks for a new generation of nanoscale electronic and optoelectronic devices. Semiconductor Nanowires: Materials, Synthesis, Characterization and Applications covers advanced materials for nanowires, the growth and synthesis of semiconductor nanowires—including methods such as solution growth, MOVPE, MBE, and self-organization. Characterizing the properties of semiconductor nanowires is covered in chapters describing studies using TEM, SPM, and Raman scattering. Applications of semiconductor nanowires are discussed in chapters focusing on solar cells, battery electrodes, sensors, optoelectronics and biology. Explores a selection of advanced materials for semiconductor nanowires Outlines key techniques for the property assessment and characterization of semiconductor nanowires Covers a broad range of applications across a number of fields
One dimensional electronic materials are expected to be key components owing to their potential applications in nanoscale electronics, optics, energy storage, and biology. Besides, compound semiconductors have been greatly developed as epitaxial growth crystal materials. Molecular beam and metalorganic vapor phase epitaxy approaches are representative techniques achieving 0D–2D quantum well, wire, and dot semiconductor III-V heterostructures with precise structural accuracy with atomic resolution. Based on the background of those epitaxial techniques, high-quality, single-crystalline III-V heterostructures have been achieved. III-V Nanowires have been proposed for the next generation of nanoscale optical and electrical devices such as nanowire light emitting diodes, lasers, photovoltaics, and transistors. Key issues for the realization of those devices involve the superior mobility and optical properties of III-V materials (i.e., nitride-, phosphide-, and arsenide-related heterostructure systems). Further, the developed epitaxial growth technique enables electronic carrier control through the formation of quantum structures and precise doping, which can be introduced into the nanowire system. The growth can extend the functions of the material systems through the introduction of elements with large miscibility gap, or, alternatively, by the formation of hybrid heterostructures between semiconductors and another material systems. This book reviews recent progresses of such novel III-V semiconductor nanowires, covering a wide range of aspects from the epitaxial growth to the device applications. Prospects of such advanced 1D structures for nanoscience and nanotechnology are also discussed.
Embodiments of the invention provide a method for direct heteroepitaxial growth of vertical III-V semiconductor nanowires on a silicon substrate. The silicon substrate is etched to substantially completely remove native oxide. It is promptly placed in a reaction chamber. The substrate is heated and maintained at a growth temperature. Group III-V precursors are flowed for a growth time. Preferred embodiment vertical Group III-V nanowires on silicon have a core-shell structure, which provides a radial homojunction or heterojunction. A doped nanowire core is surrounded by a shell with complementary doping. Such can provide high optical absorption due to the long optical path in the axial direction of the vertical nanowires, while reducing considerably the distance over which carriers must diffuse before being collected in the radial direction. Alloy composition can also be varied. Radial and axial homojunctions and heterojunctions can be realized. Embodiments provide for flexible Group III-V nanowire structures. An array of Group III-V nanowire structures is embedded in polymer. A fabrication method forms the vertical nanowires on a substrate, e.g., a silicon substrate. Preferably, the nanowires are formed by the preferred methods for fabrication of Group III-V nanowires on silicon. Devices can be formed with core/shell and core/multi-shell nanowires and the devices are released from the substrate upon which the nanowires were formed to create a flexible structure that includes an array of vertical nanowires embedded in polymer.
From quantum mechanical concepts to practical circuit applications, this book presents a self-contained and up-to-date account of the physics and technology of nanowire semiconductor devices. It includes a unified account of the critical ideas central to low-dimensional physics and transistor physics which equips readers with a common framework and language to accelerate scientific and technological developments across the two fields. Detailed descriptions of novel quantum mechanical effects such as quantum current oscillations, the metal-to-semiconductor transition and the transition from classical transistor to single-electron transistor operation are described in detail, in addition to real-world applications in the fields of nanoelectronics, biomedical sensing techniques, and advanced semiconductor research. Including numerous illustrations to help readers understand these phenomena, this is an essential resource for researchers and professional engineers working on semiconductor devices and materials in academia and industry.
Nanowires for Energy Applications, Volume 98, covers the latest breakthrough research and exciting developments in nanowires for energy applications. This volume focuses on various aspects of Nanowires for Energy Applications, presenting interesting sections on Electrospun semiconductor metal oxide nanowires for energy and sensing applications, Integration into flexible and functional materials, Nanowire Based Bulk Heterojunction Solar Cells, Semiconductor Nanowires for Thermoelectric Generation, Energy Scavenging: Mechanical, Thermoelectric, and Nanowire synthesis/growth methods, and more. Features the latest breakthroughs and research and development in nanowires for energy applications Covers a broad range of topics, including a wide variety of materials and many important aspects of solar fuels Includes in-depth discussions on materials design, growth and synthesis, engineering, characterization and photoelectrochemical studies
A timely reference from leading experts on semiconductor nanowires and their applications.