The feasibility of a templated seedless approach for growing segmented p-i-n nanowires –based diodes based on selective epitaxial growth is demonstrated. Such diodes are the basic structure for a TunnelFET device. This approach has the potential for being easily scalable at a full-wafer processing, and there is no theoretical limitation for control on nanowires growth and properties when scaling down their diameters, as opposed to an unconstrained vapor-liquid-solid growth. Moreover, Si/SixGe1-x hetero-structures are implemented, showing that this can improve the TFET ON current not only thanks to the lowered barrier for the band-to-band source-channel tunneling, but additionally thanks to its lower thermal budget for growth, allowing for better control of the abruptness of the doping profile at the source-channel tunneling interface.

In this work, SiC nanowires (NWs) were grown by chemical vapor deposition (CVD) on commercial 4H-SiC substrates. The growth was conducted in an inductively heated hot wall CVD reactor traditionally used for homoepitaxy of 4H-SiC, operating at 150 Torr with H2 as the carrier gas. The growth experiments utilized the precursor chemistry that previously enabled the so-called low-temperature homoepitaxial growth of SiC – SiCl4 as the silicon precursor and CH3Cl as the carbon precursor. Vapor-liquid-solid (VLS) growth mode was employed. Two metal catalysts Au and Ni were used for NW growth in a wide range of growth temperatures from below 10500C to above 13000C. It was established that high precursor flow rates favor the regular epitaxial growth (though disturbed by the presence of the islands of the metal catalyst) at temperatures above 12000C. Reduction of the precursor flow rates and the growth temperature caused formation of micro-needles and eventually NWs. NW diameters in the range from below 10 to 100 nm were observed using scanning electron microscopy. Only SiC phase with no presence of Si, even for the growth temperatures down to 10500C, was confirmed by X-ray diffraction.

We report a novel hybrid p-i-n heterojunction solar cell consisting of an undoped CdSe quantum dot film sandwiched between electrodeposited n-type ZnO nanowires on a compact ZnO thin film/FTO and a spin-coated hole-conducting layer. Microscopic studies show the conversion of CdSe quantum dots into conformal and continuous polycrystalline thin film coatings on ZnO nanowires upon annealing in CdCl2/ambient air. The morphology change of the CdSe quantum dot layers then provided excellent charge transfer between the absorber layer and the contiguous layers. The quantum-dot-sensitized ZnO nanostructured solar cells exhibited short-circuit current densities ranging from 5 to 10 mA/cm2 and open-circuit voltages of 0.4–0.6 V when illuminated with an 85 mW/cm2 quartz-halogen spectrum. External quantum efficiencies as high as 55–60% were also achieved.

We report here the synthesis of tin disulfide nanotubes by a vapour liquid solid growth using bismuth, a low melting metal, as a catalyst. The reaction was carried out in a single step process by heating SnS2 and bismuth in a horizontal tube furnace at 800oC. TEM analysis allowed proposing a plausible mechanism for the formation of SnS2 nanotubes. Pure material could be obtained by optimizing the reaction based on a product analysis using powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) combined with energy dispersive X-ray spectroscopy (EDX).

Optically active InP nanowires were grown on a quartz substrate covered with a layer (100 nm) of hydrogenated amorphous silicon (a-Si:H) by metalorganic chemical vapor deposition (MOCVD), demonstrating that single-crystal semiconductor nanowires can be formed on non-single-crystal surfaces. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, cathodoluminescence (CL), and photoluminescence (PL) were used to characterize the structural and optical properties of the nanowires. The nanowires on a-Si:H grew in random directions with high density. The XRD suggests that nanowires having either hexagonal-close-packed or face-centered cubic lattices co-exist. The Raman spectrum shows peaks associated with transverse optical (TO) and longitudinal optical (LO) branches of InP. The CL intensity does not vary signi?cantly along the growth direction and appears to be originated from the entire structure of the nanowire when probed at various positions. The CL data suggests that recombination is slow enough to allow the carriers to diffuse the complete length of the nanowires (˜2 m in length) before recombining. The PL spectrum suggested the nanowire had a part that contributes to the observed blue shift while the other part had nearly bulk feature in their structure.

We report on experimental results of non-resonant two-photon absorption-induced photoluminescence in ZnO nanostructures, which may act as a possible route to excite ZnO nanostructure based lasers. Epitaxial ZnO nanorod-like nanostructure was grown on pre-seeded Si (100) substrates by chemical vapor deposition (CVD) method with a mixed ZnO/C solid source. Crystalline ZnO seeds were prepared and controlled by the rapid thermal annealing (RTA) treatment of e-beam deposited amorphous ZnO thin films with various thicknesses.

The characterization of doped regions inside silicon nanowire structures poses a challenge which must be overcome if these structures are to be incorporated into future electronic devices. Precise cross-sectioning of the nanowire along its longitudinal axis is required, followed by two-dimensional electrical measurements with nanometer spatial resolution. The authors have developed an approach to cross-section silicon nanowires and to characterize them by scanning spreading resistance microscopy (SSRM). This paper describes a cleaving- and polishing-based cross-sectioning method for silicon nanowires. High resolution SSRM measurements are demonstrated for epitaxially grown and etched silicon nanowires.

ZnO nanostructures such as nanowire-networks and vertical nanorods were epitaxially grown on pre-seeded Si (100) substrates by chemical vapor deposition (CVD) method with a solid source. Crystalline ZnO seeds were prepared and controlled by the rapid thermal annealing (RTA) treatment of e-beam deposited amorphous ZnO thin films. Both epitaxially grown ZnO nanostructures and pre-deposited ZnO seeds were characterized by scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. Excellent optical characteristics of these nanostructures such as PL line width, linearity of PL intensity as a function of excitation power density were obtained.

Nanocrystalline silicon microwires are self-heated through microsecond voltage pulses. Nonlinear changes in current level are observed during the voltage pulse, which end with melting of the microwires. Liquid silicon resistivity is extracted as 65.9 ± 6.1 μΩ.cm from the minimum resistance of the wire during the voltage pulse. The extracted resistivity is in good agreement with previously reported values.

Silicon nanowire arrays grown by chemical vapour deposition were successfully integrated into functional photovoltaic devices. A crucial planarization step, achieved by embedding the nanowires in a spin-on glass matrix and subsequent polishing of the front surface, allowed to deposit a continuous and uniform conductive film on top of the nanowire array, and thus to form a high-quality front electrical contact. The silicon nanowire array solar cells fabricated using this process exhibited a parasitic series resistance as low as 5 Ω.cm2, which is a clear improvement compared to the recent literature.

We demonstrate the growth of lateral concentric BR on ZnO nano-pillars. It opens the opportunity to be used for (i) the enhancement of the lateral confinement in classical pillar-resonators in order to increase the emission rates in the regime of weak exciton-photon coupling (Purcell-effect), (ii) to enhance the exciton-polariton coupling strength in the strong-coupling regime, and (iii) to be used for two-dimensional confinement in free-standing photonic wire resonators. Spatially resolved PL experiments in dependence on the pillar diameter and on the temperature provide strong hints for the ZnO nano-pillar resonator being in the strong-coupling regime. The coupling strength can be estimated to be V = 80 meV.

The performance metrics of highly scaled n-type InSb/InP and InAs/InP core/shell nanowire (NW) field-effect transistors (FETs) are theoretically investigated using an 8-band k•p model and a semiclassical ballistic transport model. We present the ON-current, the intrinsic cut-off frequency, the gate-delay time, the power-delay product, and the energy-delay product of NWFETs with two NW diameters of 10 nm and 12 nm, which operate in the quantum capacitance limit. We compare the results to the numbers predicted or projected for other materials and dimensionalities and find good agreement. Within a source Fermi energy range of 0.1 – 0.3 eV for all devices, the ON-current varies from 7 – 58 μA, the intrinsic cut-off frequency ranges from 8 – 15 THz, the power-delay product varies from 2×10-20 – 9.7×10-19 J, the gate-delay time varies from 2 – 19 fs, and the energy-delay product ranges from 7×10-35 – 1×10-32 Js. These NWFETs, thus, provide both ultra-low power switching and high-speed.

Here we report a new in-plane solid-liquid-solid (IPSLS) mode for obtaining in-plane silicon nanowires (SiNW), which can be controlled and directly guided into various desired patterns for circuit architecture. Indium catalyst drops are firstly formed by a H2 plasma reduction of a thin layer of ITO on Corning glass substrate and then covered by an a-Si:H layer deposited at low temperature (100oC-200oC). The growth of SiNWs is activated in a reacting-gas-free thermal annealing process and led by the indium catalyst drops, that absorb and transform the a-Si:H matrix into crystalline SiNWs behind. At least two guided modes, that is, the a-Si:H channel guided mode and the step edge guided mode, can be applied to effectively control the growth routes for the lateral SiNWs. This guided growth of the IPSLS SiNWs lays an important basis for realizing various SiNWs-based device applications directly on top of low-cost substrates.

In this work we investigated the structural, electrical, and optical properties of titanium dioxide (TiO2) nanotubes (NTs) formed by electrochemical anodization of Ti metal sheets in NH4F+glycerol electrolyte at different anodization voltages (Va) and acid concentrations. Our results revealed that TiO2 NTs can be grown in a wide range of anodization voltages from 10 V to 240 V. The maximum NH4F acid concentration, at which NTs can be formed, decreases with the anodization voltage, which is 0.7% for Va<60V, and decreases to 0.1% at Va =240 V. Glancing angle X-ray diffraction (GAXRD) experiments show that as-grown amorphous TiO2 transforms to anatase phase after annealing at 400 oC, and further transforms to rutile phase at annealing temperatures above 500 oC. Samples grown in 30-120 voltage range have higher crystal quality as seen from anatase (101) peak intensity and reduced linewidth. The electrical resistivity of the NTs varies with Va concentration and increases by eight orders of magnitude when Va increases from 10 V to 240 V. This is consistent with cathodoluminescense studies which showed improved optical properties for samples grown in this voltage range. Optical properties of samples were also studied by low temperature photoluminescence. Temperature dependent I-V and photo-induced current transient spectroscopy were employed to analyze electrical properties and defect structure on NT samples.

We report the synthesis of Zn-doped TiO2 nanowires by a solution-based process. The synthesis takes place at 200°C in an alkali solution and results in both nanowire and nanoparticle precipitates. Several transmission electron microscopy techniques were used to characterize the resulting precipitates: diffraction patterns and high resolution phase contrast images provided identification of the crystalline phase of the material as well as insights into the resulting lattice parameters, energy dispersive x-ray spectroscopy allowed identification of constituent elements, and electron energy loss spectroscopy permitted quantification of relative concentrations of hydroxyl and lattice-type oxygen bonding. In addition, scanning electron microscope images provide overall perspective of the growth uniformity and morphology.

In this work, we investigated the evolution of Silicon Nanostructures with progressive annealing under different growth conditions. A structure - SixNy/a-Si/SixNy/a-Si - was grown on n-type <100> Silicon substrate using Hot Wire CVD (HWCVD) deposition technique. We report here the growth of Silicon Nanostructures by HWCVD technique with a special focus on the nature and morphology of the nanostructures with variation in growth rate and post-annealing temperature. AFM studies revealed promising results hinting at the presence of Silicon Nanostructures. With progressive annealing the morphology of the Nanostructures changed from particles to sharp pillars particularly in one of the samples elaborated in the text below. FWHM from the Confocal Raman data at room temperature was found to be 3.19 cm−1 with the a-Si peak at 520 cm−1.

The present work describes the photoconductivity dependence on ZnO nanostructure UV sensor. ZnO nanostructures were synthesized by direct vapor phase (DVP) technique. ZnO nanowires are of dimensions 30-65 nm in diameter and 5 μm in length. The role of oxygen in deciding the opto-electronic properties of nanostructured ZnO UV sensors was studied.

We report the growth of silicon nanowires (SiNWs) by chemical vapor deposition (CVD) with several catalysts. We performed low temperature photoluminescence (PL) experiments on as-grown SiNWs for the following catalysts: Au, Cu, TiSi, PdSi and PtSi. Nanowires are chemically treated with an aqua regia solution to remove the catalyst droplets, this step is followed by a thermal oxidation process. We compared the PL of as-grown and processed SiNWs for each catalyst.

Sn3O4 nanobelts were grown by a carbothermal evaporation process of SnO2 powders in association with the well known vapour-solid mechanism (VS). The nanobelts crystal structure was investigated by x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), raman spectroscopy and field emission gun scanning electron microscopy (FEG-SEM). The structural and morphological characterization has confirmed the growth of single crystal nanobelts. The electrical characterization (current-voltage, temperature-dependent resistance curves) of individual Sn3O4 nanobelts was performed at different temperatures and light excitation. The experiments revealed a semiconductor – like character as evidenced by the resistance decreasing at high temperatures. The transport mechanism was identified as the variable range hopping.

Low temperature hydrothermal methods allow for growth of nanowires on novel substrates. We examine the impact of variations in chemical concentration, time, temperature, and seed layer on nanowire (NW) growth and crystallite formation. The majority of growth (NWs and crystallites) was found to occur within the first two hours. Lower Zn(NO3)2 concentrations produced a reduction in the undesired large crystallites, whereas hexamethylene tetramine (HMT) concentration did not largely impact crystallite density or nanowire morphology. Growth temperature appeared to impact NW diameter variation. Nanowires grow only on the ZnO seed layer and crystallites seem to attach preferentially to the bare Kevlar surface.