This PDF file contains the front matter associated with SPIE Proceedings Volume XXXX, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Here we present a solution based functionalization technique for streptavidin (SA) protein conjugation to silicon nanowires (Si NWs). Si NWs, with a diameter of 110 nm to 130 nm and a length of 5 μm to 10 μm, were functionalized with 3-aminopropyltriethoxysilane (APTES) followed by biotin for the selective attachment of SA. High-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) showed that the Si NWs were conformally coated with 20 nm to 30 nm thick APTES, biotin, and SA layers upon functionalization. Successful attachment of each bio/organic layer was confirmed by X-ray photoelectron spectroscopy (XPS) and fluorescence microscopy. Fluorescence microscopy also demonstrated that there was an undesirable non-specific binding of the SA protein as well as a control protein, bovine serum albumin (BSA), to the APTES-coated Si NWs. However, inhibition of BSA binding and enhancement of SA binding were achieved following the biotinylation step. The biofunctionalized Si NWs show potential as label-free biosensing platforms for the specific and selective detection of biomolecules.

GaN-based nanowires hold great promise for solid state lighting applications because of their waveguiding properties and the ability to grow nonpolar GaN nanowire-based heterostructures, which could lead to increased light extraction and improved internal quantum efficiency, respectively. In addition, GaN nanowires can be grown directly on Si substrates, providing an inexpensive and scalable platform for device fabrication. We use finite difference time domain photonic simulations to explore light extraction efficiency enhancement in GaN nanowire-based light-emitting diodes (LEDs) on Si. Emission polarization and the placement of the emission source along the length of the nanowire were taken into consideration. We find that the optimal placement of the emission source is determined by the light reflection at the nanowire-air and nanowire-substrate interfaces and the coupling of emitted radiation into the waveguided modes, resulting in extraction efficiencies of up to 50%. Our approach to optimizing light extraction via simulation techniques can be applied to more realistic large-scale devices to guide experimental work towards nanowire-based LEDs with potentially greater efficiencies than their thin-film counterparts.

We report the fabrication and demonstration of electrically driven green, yellow-green, and amber color nanopyramid LEDs. The quantum wells were grown on nanopyramid facets, which have low polarization field and allow high In incorporation.

Indium phosphide (InP) nanowires were grown by metal organic chemical vapor deposition (MOCVD). InP nanowires grew in the structure of three-dimensional networks in which electrical charges and heat can travel over distances much longer than the mean length of the constituent nanowires. We studied the dependence of thermoelectric properties on geometrical factors within the InP nanowire networks. The InP nanowire networks show Seebeck coefficients comparable with that of bulk InP. Rather than studying single nanowires, we chose networks of nanowires formed densely across large areas required for large scale production. We also studied the role played by intersections where multiple nanowires were fused to form the nanowire networks. Modeling based on finite-element analysis, structural analysis, and transport measurements were carried out to obtain insights of physical properties at the intersections. Understanding these physical properties of three-dimensional nanowire networks will advance the development of thermoelectric devices.

We have deposited Ag metal via plasma enhanced atomic layer deposition (PEALD) and we investigated the novel optical behavior of this material. We have found that as-deposited flat PEALD Ag films exhibit unexpected plasmonic properties and the plasmonic enhancement can differ markedly, depending on the microstructure of the Ag film. Electromagnetic field simulations indicate that this plasmonic behavior is due to air gaps that are an inherent property of the mosaiclike microstructure of the PEALD-grown Ag film. We show that this material is plasmonic by itself, and when combined with previously developed dielectric core nanowires, it can produce enhancements which are two orders of magnitude greater than those reported using electroless Ag or Ag produced by e-beam deposition. We have also investigated the effect of substrate on the plasmonic enhancement, as well deposition on fabric, which results in a flexible plasmonic material.

We have employed plasma-enhanced atomic layer deposition (PEALD) as a means to create multi-layered nanocomposite structures in order to enhance the plasmonic behavior and SERS response in the detection of benzenethiol (BZT). Ag PEALD films were deposited within nanoporous anodic aluminum oxide (AAO) templates of various pore depths, using Ag(fod)(PEt₃)(fod=2,2-dimethyl-6,6,7,7,8,8,8-heptafluorooctane-3,5-dionato) as the precursor. We have examined the polycrystalline microstructure and conformality of the Ag films across the surface of an AAO template as well as into the pores, which varies significantly as thicknesses decrease. Furthermore, we investigated the plasmonic behavior of these films by performing SERS as a function of the Ag microstructure and conformality within the nanopores, using a 785 nm laser excitation and BZT as a test molecule, which forms a self-assembled monolayer on the Ag surface.

The employment of nanosized materials has gained much interest for the fabrication of field ionization gas sensors (FIGS) since they have many advantageous properties such as low cost, high sensitivity and high selectivity. In this work, we introduce a physical gas sensor using Si Nanowires (NW) configured as anode. These NWs are synthesized by using electroless etching (EE) technique, a cost effective and scaleable process for vertically aligned Si NWs. A thin layer of gold (Au) coating is subsequently applied to improve the field ionization current by introducing unoccupied local states. Characterization of pristine Si NWs and Au doped Si NWs in terms of current and voltage is done under NH₃ and O₂ gases. Our structures show more than five orders of magnitude enhanced field ionization current due to unoccupied local states formed by Au doping.

Given the large thermal activation energy of acceptors in high %Al AlGaN, a new approach is needed to control p-type conductivity in this material. One promising alternative to using impurity doping with thermal activation is using the intrinsic characteristics of the III-nitrides to activate dopants with polarization-induced charge in graded heterostructures. In this work polarization-induced activation of dopants is used in graded AlGaN nanowires grown by plasma-assisted molecular beam epitaxy to form ultraviolet light-emitting diodes. Electrical and optical characterization is provided, showing clear diode behavior and electroluminescent emission at 336nm. Variable temperature electrical measurements show little change in device performance at cryogenic temperatures, proving that dopant ionization is polarizationinduced rather than thermally activated.

In order to sustain the historic progress in information processing, transmission, and storage, concurrent integration of heterogeneous functionality and materials with fine granularity is clearly imperative for the best connectivity, system performance, and density metrics. In this paper, we review recent developments in heterogeneous integration of epitaxial nanostructures for their applications toward our envisioned device-level heterogeneity using computing nanofabrics. We first identify the unmet need for heterogeneous integration in modern nanoelectronics and review state-of-the-art assembly approaches for nanoscale computing fabrics. We also discuss the novel circuit application driver, known as Nanoscale Application Specific Integrated Circuits (NASICs), which promises an overall performance-power-density advantage over CMOS and embeds built-in defect and parameter variation resilience. At the device-level, we propose an innovative cross-nanowire field-effect transistor (xnwFET) structure that simultaneously offers high performance, low parasitics, good electrostatic control, ease-of-manufacturability, and resilience to process variation. In addition, we specify technology requirements for heterogeneous integration and present two wafer-scale strategies. The first strategy is based on ex situ assembly and stamping transfer of pre-synthesized epitaxial nanostructures that allows tight control over key nanofabric parameters. The second strategy is based on lithographic definition of epitaxial nanostructures on native substrates followed by their stamping transfer using VLSI foundry processes. Finally, we demonstrate the successful concurrent heterogeneous co-integration of silicon and III-V compound semiconductor epitaxial nanowire arrays onto the same hosting substrate over large area, at multiple locations, with fine granularity, close proximity and high yield.

Semiconducting nanowires are promising materials for a variety of applications, many of which are in optoelectronics where their ability to use quantum confinement to tune transition energy levels and their ability to epitaxially grow on substrates with large lattice-mismatches enable unique opportunities. In addition, the large relative surface area of nanowire-based devices can be either a benefit as in, for example, sensor applications or challenges such as charge trapping, non-radiative recombination or Fermi-level pinning. In this study, indium phosphide nanowires grown by metal organic chemical vapor deposition were conformally coated with aluminum oxide by atomic layer deposition as a means of controlling the surface states within the indium phosphide region. Photoluminescence spectra from the coated nanowires show a strong blueshift and slight peak broadening as compared to uncoated nanowires despite their increased lateral dimension. This degree of blueshift is unlikely to have been caused by strain associated with the coating because of its relatively thin thickness (~10 nm), and the x-ray diffraction profiles collected from the coated nanowires do not indicate the presence of substantial lattice deformation. It is more likely to be a result of altered chemical state at the surface; the uncoated nanowires have oxygen bound to both indium and phosphorus near the surface as confirmed in our X-ray photoelectron spectroscopy studies. Subsequent aluminum oxide deposition alters surface atomic bonding thereby modifying the states electronic responsible for optical properties in the nanowires.

Epitaxies of AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with different thickness of nano-scale AlN interlayers have been realized by metalorganic chemical vapor deposition (MOCVD) technology. After epitaxy, high resolution X-ray diffraction (HRXRD), temperature-dependent Hall Effect and atomic force microscopy (AFM) measurements were used to characterize the properties of these samples. First, it was found that the Al composition of AlGaN layer increases from 21.6 to 34.2% with increasing the thickness of AlN interlayer from 0 to 5 nm under the same AlGaN growth conditions. This result may due to the influences of compressive stress and Al incorporation induced by the AlN interlayer. Then, we also found that the room-temperature (RT) electron mobility stays higher than 1500 cm²/Vs in the samples within AlN interlayer thickness range of 1.5 nm, on the other hand, the low-temperature (80K) electron mobility drops dramatically from 8180 to 5720 cm²/Vs in the samples with AlN interlayer thickness increasing from 1 to 1.5 nm. Furthermore, it was found that the two-dimensional electron gas (2DEG) density increases from 1.15×10¹³ to 1.58×10¹³ cm^-2 beyond the AlN interlayer thickness of 1 nm. It was also found that the temperature independent 2DEG densities are observed in the samples with AlN interlayer thickness of 0.5 and 1 nm. The degenerated characteristics of the samples with AlN thickness thicker than 1.5 nm show the degraded crystalline quality which matched the observation of surface defects and small cracks formations from their AFM images. Finally, the 2DEG mobilities of the proposed structures can be achieved as high as 1705 and 8180 cm²/Vs at RT and 80K, respectively.

In this paper, high aspect ratio vertically oriented p-silicon (100) micropillars and microwalls were fabricated using the deep reactive ion etching (DRIE) process with the BOSCH recipe of cyclical passivation and etching. Two different patterns were etched; uniform pillar arrays of dimensions ~15µm (height) x 2µm (diameter) and wall arrays of dimensions ~1.5µm (width) x 25µm (height). Three-dimensional (3D) heterostructures of n-ZnO/p-Si heterostructures were fabricated from growing hydrothermally dense arrays of ZnO nanowires (290-400 nm in length and 48-80 nm in diameter) and depositing Aluminum-ZnO (AZO) thin film onto the high aspect ratio vertically oriented p-silicon micropillars and microwalls. The performances of the fabricated heterostructure optoelectronic devices were characterized for different applications including solar cells, photodetectors and field ionization gas sensors.

We have investigated electrical properties of indium phosphide nanowire field effect transistors with four different types of metal electrodes (Cr, Ti, Au, and Pt). The nanowires with a width of 50 nm were undoped and grown by metal-organic chemical vapor deposition. Among the four types of metal electrodes, Cr/InP and Ti/InP showed ambipolar conduction, while Pt/InP and Au/InP exhibited p-type conduction. Extracted Schottky barrier heights suggest that barrier heights do not vary linearly with respect to the metal workfunction. Although the Pt/InP features the smallest barrier height, the Au/InP showed the highest drain current at a given gate bias.