Single Semiconductor Nanowires Research Articles

Engineering Parallel and Perpendicular Polarized Photoluminescence from a Single Semiconductor Nanowire by Crystal Phase Control

We report on a crystal phase-dependent photoluminescence (PL) polarization effect in individual wurtzite GaAs nanowires with a zinc blende GaAsSb insert grown by Au-assisted molecular beam epitaxy. The PL emission from the zinc blende GaAsSb insert is strongly polarized along the nanowire axis while the emission from the wurtzite GaAs nanowire is perpendicularly polarized. The results indicate that the crystal phases, through optical selection rules, are playing an important role in the alignment of the PL polarization in nanowires besides the linear polarization induced by the dielectric mismatch. The strong excitation power dependence and long recombination lifetimes ( approximately 4 ns) from the wurtzite GaAs and zinc blende GaAsSb-related PL emission strongly indicate the existence of type II band alignments in the nanowire due to the presence of nanometer thin zinc blende segments and stacking faults in the wurtzite GaAs barrier.

Evidence for surface states in a single 3 nm diameter Co3O4 nanowire

The electronic local density of states of a single Co3O4 semiconductor nanowire with the diameter of 3 nm is explored using low-temperature scanning tunneling microscopy and spectroscopy. The energy gap between the conduction band and valence band of the nanowire is about 1.7 eV, which is slightly enhanced compared to the bulk value, ∼1.5 eV, due to the quantum confinement effect. Two surface states are observed locating near the Fermi level in the band gap.

Insights into single semiconductor nanowire heterostructures using time-resolved photoluminescence

We review a number of time-resolved photoluminescence experiments which have provided new understanding of the physical properties of single nanowires and single semiconductor nanowire heterostructures. Specifically, TRPL spectroscopy has been used to understand more fully non-radiative surface and bulk defects, radiative defects in CdS, InP and GaAs nanowires, core-shell effects, polytypism in InP nanowires, many body effects in GaAs and InP nanowires, and type-II band alignments in ZB/WZ mixed phase nanowires.

Orientation‐Dependent Optical‐Polarization Properties of Single Quantum Dots in Nanowires

The absorption and emission polarization of single semiconductor nanowire quantum dots is studied. The polarization of light absorbed or emitted by such dots strongly depends on the orientation of the nanowire with respect to the directions along which light is incident or emitted (see image). This result is vital for photonic applications based on quantum dots, such as generation of entangled photons.

Combined optical trapping and microphotoluminescence of single InP nanowires

In this letter, we demonstrate that microphotoluminescence may be combined with optical trapping for effective optical characterization of single target InP semiconductor nanowires in suspension. Using this technique, we may investigate structural properties of optically trapped nanowires, such as crystalline polytypes and stacking faults. This arrangement may also be used to resolve structural variations along the axis of the trapped nanowire. These results show that photoluminescence measurements may be coupled with optical tweezers without degrading the performance of the optical trap and provide a powerful interrogation tool for preselection of components for nanowire photonic devices.

Magnetic Property and Spatial Occupation of Co Dopants in Zn0.98Co0.02O Nanowires

Single phase Co-doped ZnO dilute magnetic semiconductor nanowire was synthesized by a chemical solution method and characterized by X-ray absorption fine structure (XAFS). The Co K-edge XAFS spectroscopy reveals that the doped Co ions are substantially incorporated into the ZnO host lattice. Moreover, the spatial occupation of Co dopants in Zn0.98Co0.02O nanowire is resolved further by the detailed O K-edge XANES analysis. We suggest that the Co ions are randomly doped into the ZnO matrix and located at the Zn sites. The magnetization measurement of the Co-doped ZnO nanowire shows the room temperature ferromagnetic characteristic with a relatively larger saturation magnetization. Furthermore, we suggest that the enhanced ferromagnetism can be ascribed to the coeffect of the size effect and the homogeneity of Co dopants for Zn0.98Co0.02O nanowire, which will make it useful in nanometer spintronic devices.

16.2: Invited Paper: Flexible/Stretchable Electronics for Unusual Display Systems

AbstractOrganized arrays of single crystalline semiconductor nanoribbons, nanomembranes and nanowires represent an enabling class of thin film type material for flexible/stretchable circuits suitable for display and other applications. This paper describes methods to create and manipulate such materials, and a variety of device demonstrators to illustrate key capabilities.

Field-Effect Modulation of Seebeck Coefficient in Single PbSe Nanowires

In this Letter, we present a novel strategy to control the thermoelectric properties of individual PbSe nanowires. Using a field-effect gated device, we were able to tune the Seebeck coefficient of single PbSe nanowires from 64 to 193 microV x K(-1). This direct electrical field control of sigma and S suggests a powerful strategy for optimizing ZT in thermoelectric devices. These results represent the first demonstration of field-effect modulation of the thermoelectric figure of merit in a single semiconductor nanowire. This novel strategy for thermoelectric property modulation could prove especially important in optimizing the thermoelectric properties of semiconductors where reproducible doping is difficult to achieve.

Surface exciton-plasmon polariton enhanced light emission via integration of single semiconductor nanowires with metal nanostructures

The light emission enhancement behavior from single ZnO nanowires integrated with metallic contacts is investigated by micro-photoluminescence measurements. Apart from surface plasmon polaritons at the air/metal interface, the emission of a single ZnO nanowire can be coupled into guided modes of surface excitonplasmon polaritons (SEPPs). The out-coupling avenues of SEPP guided modes are modeled in the presence of nanostructures, such as corrugation and gratings, on the metal surface. The guided modes of SEPPs in metalcontacted ZnO nanowires are calculated using the effective index method. The enhanced light emission from single semiconductor nanowires shows promise for use in highly efficient nano-emitters and nano-lasers, as well as macroscopic solid state light sources with very high efficiency.

Modification of the photoluminescence anisotropy of semiconductor nanowires by coupling to surface plasmon polaritons

We demonstrate efficient modification of the polarized light emission from single semiconductor nanowires by coupling this emission to surface plasmon polaritons on a metal grating. The polarization anisotropy of the emitted photoluminescence from single nanowires is compared for wires deposited on silica, a flat gold film, and a shallow gold grating. By varying the orientation of the nanowire with respect to the grating grooves, the large intrinsic polarization anisotropy can be either suppressed or enhanced. This modification is interpreted by the appearance of an additional emission channel induced by surface plasmon polaritons and their conversion to p-polarized radiation at the grating.

Semiconductor nanowires: optics and optoelectronics

Single crystalline semiconductor nanowires are being extensively investigated due to their unique electronic and optical properties and their potential use in novel electronic and photonic devices. The unique properties of nanowires arise owing to their anisotropic geometry, large surface to volume ratio, and carrier and photon confinement in two dimensions (1D system). Currently, tremendous efforts are being devoted to rational synthesis of nanowire structures with control over their composition, structure, dopant concentration, characterization, fundamental properties, and assembly into functional devices. In this article we will review the progress made in the area of nanowire optics and optoelectronic devices, including diodes, lasers, detectors, and waveguides, and will outline the general challenges that must be overcome and some potential solutions in order to continue the exponential progress in this exciting area of research.

Composition analysis of single semiconductor nanowires using pulsed-laser atom probe tomography

We report the composition analysis of single InAs and Si semiconductor nanowires using pulsed-laser atom probe tomography. The experimental conditions and sample geometries needed to realize 3-D composition mapping are described in detail. InAs mass spectra obtained using voltage pulses and laser pulses are compared, and are found to be superior for pulsed-laser evaporation. The ability to analyze intrinsic Si nanowires using pulsed laser evaporation is demonstrated. No peaks associated with the gold catalyst used were found in the InAs or the Si nanowire mass spectra.

Broadband ZnO Single-Nanowire Light-Emitting Diode

We present a novel technique for reliable electrical injection into single semiconductor nanowires for light-emitting diodes and lasers. The method makes use of a high-resolution negative electron-beam resist and direct electron-beam patterning for the precise fabrication of a metallic top contact along the length of the nanowire, while a planar substrate is used as a bottom contact. It can be applied to any nanowire structure with an arbitrary cross section. We demonstrate this technique by constructing the first zinc oxide single-nanowire light-emitting diode. The device exhibits broad sub-bandgap emission at room temperature.

Synthetic Control of the Diameter and Length of Single Crystal Semiconductor Nanowires

A general synthetic method has been developed to control both the diameter and the length of nanowires during growth. This approach exploits monodisperse nanocluster catalysts to define both the nanowire diameter and the initiation of nanowire elongation during growth by a vapor−liquid−solid mechanism. To demonstrate this new approach, crystalline indium phosphide (InP) nanowires have been synthesized using a laser catalytic growth (LCG) process combined with gold nanocluster catalysts. InP nanowires with nearly monodisperse diameters of 10, 20, and 30 nm were grown from nanocluster catalysts having diameters of 10, 20, and 30 nm, respectively. High-resolution transmission electron microscopy studies show that the InP nanowires prepared in this manner are single crystals with a [111] growth direction. In addition, studies of nanowire growth as a function of growth time have shown that nanowire length is directly proportional to growth time and have enabled the preparation of InP nanowires with narrow length distributions centered at 2, 4, 6, and 9 μm. The new level of synthetic control afforded by our approach should enable better-defined fundamental studies of nanowires and open up new opportunities for the assembly of functional nanodevices.

Electron-beam melting and evaporation of metals and non-metals

Single semiconductor nanowires offer an attractive option for low-cost and high-efficiency with diverse applications in sensing, photodetecting, and light-harvesting. One of the crucial goals for the single-nanowire-based devices is to find the most effective strategies to realize broadband and high optical absorption. We demonstrate in this study that integrating a nanovoid resonator into the single nanowire can substantially enhance the absorption to sunlight by exciting highly strengthened optical resonances in the nanovoid-deformed nanowire cavity. Without considering the factor of the reduced photoactive material, the photocurrent density of the single-nanowire solar absorber under the asymmetrical nanovoid design can be improved by ~37.5% over that based on the conventional solid nanowire devices. Moreover, the high absorption can be well preserved by either filling the nanovoid with low-index dielectric or introducing the dielectric substrate. This study advances our understanding on how the sunlight can be effectively manipulated by a nanovoid in high-index semiconductor nanostructures and provides an inspiring strategy to realize highly efficient photovoltaic devices.