This book, the second of two volumes, describes heterostructures and optoelectronic devices made from GaN and ZnO nanowires. Over the last decade, the number of publications on GaN and ZnO nanowires has grown exponentially, in particular for their potential optical applications in LEDs, lasers, UV detectors or solar cells. So far, such applications are still in their infancy, which we analyze as being mostly due to a lack of understanding and control of the growth of nanowires and related heterostructures. Furthermore, dealing with two different but related semiconductors such as ZnO and GaN, but also with different chemical and physical synthesis methods, will bring valuable comparisons in order to gain a general approach for the growth of wide band gap nanowires applied to optical devices.

GaN and ZnO nanowires can by grown using a wide variety of methods from physical vapor deposition to wet chemistry for optical devices. This book starts by presenting the similarities and differences between GaN and ZnO materials, as well as the assets and current limitations of nanowires for their use in optical devices, including feasibility and perspectives. It then focuses on the nucleation and growth mechanisms of ZnO and GaN nanowires, grown by various chemical and physical methods. Finally, it describes the formation of nanowire heterostructures applied to optical devices.

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.

Abstract: Over the past 15 years, nanowires (NWs) and nanotubes have drawn great attention since the application of VLS growth mechanism into the synthesis of one dimensional structures. Semiconductor nanowires exhibit novel electrical and optical properties. With a broad selection of composition and band structures, these one-dimensional semiconductor nanostructures are considered to be the critical components in a wide range of potential nanoscale device applications. To fully exploit these one-dimensional nanostructures, current research has focused on synthetic control of one-dimensional nanoscale building blocks, characterization of their novel properties, device fabrication based on nanowire building blocks, and integration of nanowire elements into complex functional architectures. Progress has been made in past two decades. However, there are still challenges in NWs growth controls, such as size, shape, position, stoichiometry and defects. Due to the dimensionality and possible quantum confinement effects of nanowires, there are also challenges in characterization and device fabrication. A systematic study of controlled growth of nanowires has been conducted in this dissertation. The first part of this dissertation presents various synthesis techniques of semiconductor nanowires via metal catalyzed vapor-liquid-solid (VLS) growth mechanism. Pulse laser deposition (PLD) with arsenic over pressure method has been successfully utilized for GaAs nanowires. Challenges such as uniformity issue commonly seen in MOCVD and MBE systems, morphology and stoichiometry issues commonly seen in conventional PLD systems have been overcome. Si nanowires fabrication via ultrahigh vacuum magnetron sputtering has reported for the first time, which also provides an alternate route for Si nanowires synthesis. The second part of this dissertation discusses optical properties of ensemble direct band gap nanowires. Photoluminescence spectra have been measured on an ensemble of random orientated InP nanowires. Polarization anisotropy has been explored on ensemble nanowires and oxide-coated nanowires. Our calculation for randomly oriented nanowires agrees well with experimental results. The control of polarization anisotropy of nanowires is realized by coating nanowires with an oxide layer composed of matching dielectric constant media. This opens a path to optical spin injection and detection on direct band gap nanowires.

Volume 1, Metal and Semiconductor Nanowires covers a wide range of materials systems, from noble metals (such as Au, Ag, Cu), single element semiconductors (such as Si and Ge), compound semiconductors (such as InP, CdS and GaAs as well as heterostructures), nitrides (such as GaN and Si3N4) to carbides (such as SiC). The objective of this volume is to cover the synthesis, properties and device applications of nanowires based on metal and semiconductor materials. The volume starts with a review on novel electronic and optical nanodevices, nanosensors and logic circuits that have been built using individual nanowires as building blocks. Then, the theoretical background for electrical properties and mechanical properties of nanowires is given. The molecular nanowires, their quantized conductance, and metallic nanowires synthesized by chemical technique will be introduced next. Finally, the volume covers the synthesis and properties of semiconductor and nitrides nanowires.

"Semiconductor nanowires exhibit novel electronic and optical properties due to their unique one-dimensional structure and quantum confinement effects. In particular, III-V semiconductor nanowires have been of great scientific and technological interest fo"