Semiconductor nanowires and nanotubes: Synthesis to devices

One-dimensional nanostructures, including nanowires and nanotubes, are a promising class of basic building blocks for future optical, electronic, nanofluidic, thermoelectric, and energy conversion devices. These nanowire materials are ideal, single-crystalline semiconductors that represent a facile route toward sub-100 nm features that cannot be easily fabricated through lithographic means. This dissertation describes numerous proof-of-concept studies detailing the synthesis of single-crystalline inorganic nanowire and nanotube materials, characterization of their optical and electrical properties, and their integration into novel device applications.; First, a novel "epitaxial casting" technique is developed to enable the synthesis of single-crystalline nanotube materials from materials with bulk crystal structures that have a traditional ionic lattice crystal structure. In this technique, ZnO nanowires are used as sacrificial templates for the epitaxial deposition of the desired nanotube material (GaN). The nanowire template is then dissolved away. The resultant nanotubes are seamless single-crystalline materials, lack pinholes, they are mechanically robust, electrically active, and have a high optical quality, with little defect emission. These nanotubes represent a novel platform for the experimental study of nanofluidic transport of ions and biomolecules in a previous inaccessible size regime (3-100 nm).; The second part of this dissertation details the electrical property characterization of ZnO and GaN nanowire materials and their application into planar electronic devices including transistors, photodetectors, and light emitting diode arrays. These nanowire materials are readily and reliably incorporated as the active semiconductor channels in a planar, three-terminal field effect transistor geometry. Device properties such as mobility and carrier concentration are extracted. These ZnO transistor devices have among the highest mobility values for all ZnO transistors previously fabricated. Additionally, the performance characteristics of the nanowire transistors were found to be intimately tied to the presence and nature of adsorbed surface species, making these materials extremely useful for chemical sensing applications. This thorough characterization allows the integration of these nanowire materials into numerous optical, electronic applications, including devices for light sensing, utilizing the photoconductive properties of ZnO nanowires, and light emission, in light-emitting diodes using GaN nanowires.; Finally, the reliable, cost-effective integration of these nanowire elements into ultra-high density transistor devices still remains as one of the biggest technological hurdles preventing their direct application. To overcome this problem, a novel approach was developed towards the integration of silicon nanowires into vertical field effect transistors having a surrounding gate geometry without the need for any expensive postgrowth assembly processes. This is accomplished through the controlled, epitaxial synthesis of vertically aligned silicon nanowire arrays from silicon (111) substrates. These nanowire arrays have narrow diameter distributions dictated by the distribution of the seeding colloids. Additionally, the growth position of these nanowire materials can be controlled via accurate placement of these nanoparticle catalysts. The direct vertical integration of these nanowire arrays into surrounding gate field effect transistors is accomplished using conventional very-large-scale-integration processing. This surrounding-gate geometry is the ideal electrostatic gating geometry for the expected minimization of power consumption. The device fabrication allows Si nanowire channel diameters to be readily reduced to the 5-nm regime. These first-generation vertically integrated nanowire field effect transistors (VINFETs) exhibit electronic properties that are comparable to other horizontal nanowire field effect tr...