| Semiconductor nanowires can function both as active electrical components and as efficient conduits for the transport of charge carriers, and hence represent unique nanoscale building blocks for electronic and optoelectronic devices. This thesis presents a general approach to the controlled synthesis of nanowires and nanowire heterostructures, the characterization of their physical properties, and efforts towards developing “nanotechnology-enabled” devices.; Monodisperse nanocluster catalysts were used to define the nanowire diameter and (through growth time) the length of gallium phosphide, indium phosphide, and silicon nanowires via the vapor-liquid-solid (VLS) mechanism. The vapor phase semiconductor reactants were introduced either by laser ablation of solid targets or by gaseous molecular species in the presence of substrates functionalized with monodisperse gold colloid catalysts to direct the growth.; The diameter-dependent optical properties of single indium phosphide nanowires were examined via photoluminescence using epifluorescence microscopy. Studies of nanowires with diameters from 10–50 nm revealed a systematic blue-shift in the emission as a function of decreasing nanowire diameter and fits of the data to an effective mass model showed the data to be consistent with radial confinement of the excitons. Polarization dependent measurements revealed photoluminescence anisotropy considerably larger than seen in previous optical studies of epitaxially grown nanowires. This effect was modeled quantitatively by treating the nanowire as an infinite dielectric cylinder in a vacuum, illustrating that the large polarization effects arise from the dielectric contrast of the nanowire with its air (vacuum) surroundings. Furthermore, single nanowire photocurrent measurements validated this model and demonstrated that nanowires can function as nanoscale polarization-sensitive photodetectors.; While the study of single component systems is important to the development of nanowire-based technologies, most advanced semiconductor technologies are based upon junctions between different materials. Modulation of the semiconductor reactants during VLS growth yielded single and multiple junctions along the axis of individual nanowires. Characterization of these nanowires demonstrated their functionality as nanoscale optical barcodes, p-n junctions, and polarized nanoscale light emitting diodes. The growth of radial junctions was explored next. Silicon and germanium were used to synthesize core-shell modulation-doped nanowires and nanowire heterostructures. These core-shell approaches were utilized to demonstrate transistors and explore various device geometries.; Lastly, there is a discussion of the anomalous electron diffraction seen in silicon and germanium nanowires. These 1/3{lcub}422{rcub} reflections, although forbidden in bulk crystals, are general to nanoscale cubic crystals when measured on the [111] zone axis. (Abstract shortened by UMI.)... |
